You can use the VB resource inside of the own MS Excel to build macros, but you can also do a lot of damage and a lot of good with it outside of Excel.
Bradley Paul Neal (his name is spelled out here because I suffer true atrocities since the end of 2001 for denouncing ALSO him) once showed me how to hack Yahoo accounts and get passwords. He then entered VB through Excel and made a perfect copy of the Yahoo main access page.
He edited the page because, at least until 2002, it had an open code. He then changed a few lines (less than five, perhaps just one) and showed me that the person would think that the computer had a problem and they would be filling out the fields. On the first time already we would get the password stored in an Excel file that would, later on, be picked through a disk by him. I actually found an Excel file with my name on it, marcia.xls, exactly in the way he had described to me that he did, when I was sharing a room with Shane and Robert at VUT, and I then took that file to Judith Cook as a material proof against him.
Oh, well, that is an evil use of the tool, we could say.
If you want to do some good, however, you will probably want to start working by entering the developers' mode. The first thing you will need to know, in this case, is how to get into the developers' mode. So, here you have the how to do that: Developers