Hi and welcome to the forum

This is a pretty easy task you can achieve what you need using the vlookup() function. the syntax is...
=VLOOKUP(what-you-want-to-find,range-to-search-in,column-that-contains-the-match,FALSE) FALSE is for finding an exact match

I would suggest that (if you can) put both lists into 1 workbook - same of different work sheets, doesnt matter, and actually, you can do this between different workbooks too.

If you still have a problem, i would suggest you upload a sample work book, (all sensitive data removed), showing what data you are working with, a few examples of what your expected outcome is, and how you arrived at that
To attach a file to your post,
click advanced (next to quick post),
scroll down until you see "manage file",
click that and select "add files" (top right corner).
click "select files" find your file, click "open" click "upload" click 'done" bottom right. click "submit reply"

Once the upload is completed the file name will appear below the input boxes in this window.
You can then close the window to return to the new post screen.