Getting started with functions (Programming?)

I want to automate a spreadsheet that has multiple customer sheets containing quotes and purchase orders. I'd like to open the sheet and be prompted for "which customer" to select the correct sheet, then be shown an input interface that will ask "Quote" or "PO", then prompt me for several fields which will be added to the next line in the spreadsheet.

My question is, what "subjects" do I need to search for in Excel Help, and if there are [short] books, particular forums, and/or tutorials out there, please point me in the right direction. I have been using Excel for years, but never had a need to venture into anything but the simplest, single sheet functions. Now I use it to track my quotes and purchase orders throughout the quarters of the year, with simple totals by each quarter, half, and full year.

I just joined up, have done a cursory scan of the different forums here, and will continue to search and visit the Q&A section. So, what topic do I need to read up on first?

Appreciate any pointers and recommendations. Thank you!

Thanks shg,
I will look for it. I also looked at the Excel version installed on our work issued laptops; Excel 2002! However, there is a possibility I can download and install 2003 from our internal repsoitory. Anyway...

Thank you.