How to Copy User defined columns from one workbook to another

Hello, please help me out on my macro!
I just started using VBA programming for work and I have a very large macro to write.
The concept is, I have a main master workbook where all the data is collected and then manipulated. I will be collecting the data from two other source workbooks, both in different formats. These source workbooks are going to updated weekly.

PROBLEM: I want to be able to copy columns from one of the source workbooks and paste into the master workbook. However, because this is rather a big and meticulous project, I need to be able to have the user specify the columns (this could be satisfied with searching for the column names, as these would be known) and then to have the user specify which sheet of the master workbook that the selected columns will be pasted.

The code I have is huge and messy and I haven't attempted to run it yet. Its a mixture of me recording a macro and adding in my own code to clean it up. It does not include code to get the user input on what columns to copy (I have no idea how to do that one) but I do have code on how to get a user specified worksheet. I have posted it if people want to take a look, but I will guarantee that it is hard to interpret, mostly because there is a lot of code in there that smart people would have simplified.

More clarification: There will always be multiple columns selected and these will be different each time depending on which sheet is selected to paste them into. The source sheets have hourly&daily electricity meter readings for 50 different buildings. I am making groups of buildings (ex. group1 will have 4 buildings) and giving each group their own sheet in the master workbook (group1 = sheet1, group2 = sheet2, etc.). All the sheets are pre-named.

I hope all of this makes sense. Please help me out, I have already been working on this bad boy for three days straight.

Sub Data_analysis()
'
' This macro will open a user specified workbook
' Then data will be collected from the source workbook and pasted into ThisWorkBook
' The data will then be manipulated for statistical purposes.
' ThisworkBook should be updated weekly with new data from a source workbook.
' The new weekly data should APPEND to the existing data in thisworkbook. I haven't figured that one yet either
'
    Dim wbsource1 As Workbook
    'Dim wbsource2 As Workbook
    Dim ws1 As Worksheet
    'Dim lastrow As Long, lastcol As Long
    Dim Ret1, Ret2
    Dim i As Integer
    
    Set ThisWorkbook = ActiveWorkbook
        
    'lastrow = .Cells(Rows.Count, "A").End(xlUp).Row
    'lastcolumn = .Cells(1, Columns.Count).End(xlToLeft).Column
    
    '~~> Get the first File
    Ret1 = Application.GetOpenFilename("Excel Files (*.xlsx*), *.xlsx*", _
    , "Please select first file")
    If Ret1 = False Then Exit Sub
    
    '~~> Get the 2nd File
    'Ret2 = Application.GetOpenFilename("Excel Files (*.xlsx*), *.xlsx*", _
    , "Please select Second file")
    'If Ret2 = False Then Exit Sub
    
    Set wbsource1 = Workbooks.Open(Ret1)
    'Set ws1 = wbsource1.Sheets(1)
    'wbsource1.Activate
    Columns("A:A").Select
    Selection.Copy
    
    ThisWorkbook.Activate
    'Get the user specified sheet to paste timestamps in
    myShts = ThisWorkbook.Sheets.Count
    For i = 1 To myShts
    myList = myList & i & " - " & ThisWorkbook.Sheets(i).Name & " " & vbCr
    Next i
    Dim mySht As Single
    mySht = InputBox("Select sheet to go to." & vbCr & vbCr & myList)
    Sheets(mySht).Select
        
    'Paste time stamps in the first column. This code may change depending on how the data is received.
    ' If the data is just given per week, than I have to change it so that the data appends to the end
    ' of the first column.
    Range("A1").Select
    ActiveSheet.Paste
    ThisWorkbook.Save
    
    'Copy energy data from source to be pasted in thisworkbook
    'This is where I want the use to specify which columns to copy
    wbsource1.Activate
    Columns("C:E").Select
    Application.CutCopyMode = False
    Selection.Copy
    
    ' Paste data into column D.
    ' If the data is just given per week, than I have to change it so that the data appends to the end
    ' of the first column.
    ThisWorkbook.Activate
    Range("D1").Select
    ActiveSheet.Paste
    
    'Manipulating timestamp data to display date only, both columns B and C
    Range("B2").Select
    Application.CutCopyMode = False
    ActiveCell.FormulaR1C1 = "=TEXT(RC[-1], ""dd-mm-yy"")"
    Range("B2").Select
    Selection.AutoFill Destination:=Range("B2:B4135"), Type:=xlFillDefault
    Range("B2:B4135").Select
    ActiveWindow.ScrollRow = 2
    Range("C2").Select
    ActiveCell.FormulaR1C1 = "=LEFT(RC[-1], 5)"
    Range("C2").Select
    Selection.AutoFill Destination:=Range("C2:C4135"), Type:=xlFillDefault
    Range("C2:C4135").Select
    ActiveWindow.ScrollRow = 2
    
    'Add in the single date column to sum up the time intervals
    Range("I2").Select
    ActiveCell.FormulaR1C1 = "23-10"
    Range("I3").Select
    ActiveCell.FormulaR1C1 = "24-10"
    Range("I4").Select
    ActiveCell.FormulaR1C1 = "25-10"
    
    Range("I5:I10").Select
    Selection.NumberFormat = "General"
    Range("I5").Select
    ActiveCell.FormulaR1C1 = "26-10"
    Range("I6").Select
    ActiveCell.FormulaR1C1 = "27-10"
    Range("I7").Select
    ActiveCell.FormulaR1C1 = "28-10"
    Range("I8").Select
    ActiveCell.FormulaR1C1 = "29-10"
    Range("I9").Select
    ActiveCell.FormulaR1C1 = "30-10"
    Range("I10").Select
    ActiveCell.FormulaR1C1 = "31-10"

    Range("I11:I39").Select
    Selection.NumberFormat = "@"
    Range("I11").Select
    ActiveCell.FormulaR1C1 = "01-11"
    Range("I12").Select
    ActiveCell.FormulaR1C1 = "02-11"
    Range("I13").Select
    ActiveCell.FormulaR1C1 = "03-11"
    Range("I14").Select
    ActiveCell.FormulaR1C1 = "04-11"
    Range("I15").Select
    ActiveCell.FormulaR1C1 = "05-11"
    Range("I16").Select
    ActiveCell.FormulaR1C1 = "06-11"
    Range("I17").Select
    ActiveCell.FormulaR1C1 = "07-11"
    Range("I18").Select
    ActiveCell.FormulaR1C1 = "08-11"
    Range("I19").Select
    ActiveCell.FormulaR1C1 = "09-11"
    
    Range("I19").Select
    Selection.AutoFill Destination:=Range("I19:I22"), Type:=xlFillFormats
    Range("I19:I22").Select
    Range("I20").Select
    ActiveCell.FormulaR1C1 = "10-11"
    Range("I21").Select
    ActiveCell.FormulaR1C1 = "11-11"
    Range("I22").Select
    ActiveCell.FormulaR1C1 = "12-11"
    Range("I23").Select
    ActiveCell.FormulaR1C1 = "13-11"
 
    Range("I24").Select
    ActiveCell.FormulaR1C1 = "14-11"
    Range("I25").Select
    ActiveCell.FormulaR1C1 = "15-11"
    Range("I26").Select
    ActiveCell.FormulaR1C1 = "16-11"
    Range("I27").Select
    ActiveCell.FormulaR1C1 = "17-11"
    Range("I28").Select
    ActiveCell.FormulaR1C1 = "18-11"
    Range("I29").Select
    ActiveCell.FormulaR1C1 = "19-11"
    Range("I30").Select
    ActiveCell.FormulaR1C1 = "20-11"
    Range("I31").Select
    ActiveCell.FormulaR1C1 = "21-11"
    Range("I32").Select
    ActiveCell.FormulaR1C1 = "22-11"
    Range("I33").Select
    ActiveCell.FormulaR1C1 = "23-11"
    Range("I34").Select
    ActiveCell.FormulaR1C1 = "24-11"
    Range("I35").Select
    ActiveCell.FormulaR1C1 = "25-11"
    Range("I36").Select
    ActiveCell.FormulaR1C1 = "26-11"
    Range("I37").Select
    ActiveCell.FormulaR1C1 = "27-11"
    Range("I38").Select
    ActiveCell.FormulaR1C1 = "28-11"
    Range("I39").Select
    ActiveCell.FormulaR1C1 = "29-11"
    Range("I40").Select
    ActiveCell.FormulaR1C1 = "30-11"
    
    Range("I41:I45").Select
    Selection.NumberFormat = "@"
    Range("I41").Activate
    ActiveCell.FormulaR1C1 = "01-12"
    Range("I42").Activate
    ActiveCell.FormulaR1C1 = "02-12"
    Range("I43").Select
    ActiveCell.FormulaR1C1 = "03-12"
    Range("I44").Select
    ActiveCell.FormulaR1C1 = "04-12"
    
    'Add in the data manipulation for the total daily energy value
    ActiveWindow.SmallScroll Down:=-48
    Range("J2").Select
    ActiveCell.FormulaR1C1 = "=SUMIF(C3, RC9,C[-6] )"
    Range("J2").Select
    Selection.AutoFill Destination:=Range("J2:L43"), Type:=xlFillDefault
    Range("J2:L43").Select
    
    ActiveWindow.SmallScroll Down:=-27
    Range("M2").Select
    ActiveCell.FormulaR1C1 = "=IF(C[-10]=RC[-4], R[94]C[-6]-RC[-6])"
    Range("M2").Select
End Sub