How to create a macro to combine cell values?

Hello,

I am new to excel and I am trying to create macro for a spreadsheet where I can go through a list of 4000+ entries. What I have is column A is "Store Number" and column B is "Item Number", there will be repeat store numbes in column A. I need the macro to go through column A and search for all the same store numbers and copy the items numbers in column B and combine them together so there is only store number with a list of item numbers (this can be placed in Column D and E).

Can anyone help me with this? Thanks!

M