how to insert file path of every file in a folder as a string?

Hello everyone, I've got a small problem and I can't figure out how to fix it (especially because I normally don't ever use Excel), but let me explain my problem first:
In the cells A1 and B2 I saved the names of two variables, cells A2-A50 is filled with consecutive numbers (#1, #2, etc.).
These numbers represent the number of a picture in a certain folder on my PC, and now I have to put the file-paths of the pictures in the cells B1-B50.
Fifty is just an example, the whole thing is supposed to hold as many pictures as needed (in some cases that could be over one thousand pictures) - individual pasting of the values is a no go here.
My first idea was to change the name of the images via the rename-function of windows, so that the pictures now have the file-path "C:\folder\picture(1)" - "C:\folder\picture(50)".
I pasted the path in the first three cells of a column and hoped that Excel would recognize the pattern, but it didn't.
My second idea was to use something like Length, Replace and CharAt or something like that, but like I said, I have never used Excel. Another idea was to use a variable in between the brackets, but I don't know how to do that (the file may not get additional columns and the first column has to keep the '#' in front of the numbers).
Also I need to save the whole file as a .csv and the file-paths are supposed to be a STRING-type in the end.

I'm completely out of ideas, I googled for a while, but it looks like no one had a problem like that before, or maybe they had, but I'm searching for the wrong things.

Can someone help me? I would really appreciate it