Module vs Object

May someone please kindly reply my initial question:

what is the different to have my Excel VBA codes in "Module" vs "The Workbook" which both can be found in the Project Window located on the top left corner by default.

May the explanation will be using the simplest example: if I were to use the Msgbox of:

Sub x()
Msgbox "Hi"
End Sub

what is the different to add it in The Workbook compare with in The Module?

Now I think I got another problem, accordingly to Shg, I shall change me flag. I read the rule but don get what I suppose to change. I am to study. Hope someone can give me the most direct way to change me flag.....ok for those who are new like me....just click the yellow icon on the top (after the bold, italic....)...hope this is what shg is referring.

remark: thanks to those who are sincerely help by providing direct answer and not attempting to show off by talking "cool" yet not helping.