The resources below are some of the sites most likely to give you good results when you search for Excel help on google.
Mr Excel -
http://www.mrexcel.com/forum/ – a good forum – most useful if you have a specific question you google and this pops up as having an answer. I've never posted anything here.
Contextures -
http://blog.contextures.com/– a blog with good explanations
Tech on the Net -
http://www.techonthenet.com/excel/index.php– shows formulas with basic explanations, not great for examples
Stack Overflow -
http://stackoverflow.com/questions/tagged/excel– another forum, hit or miss on useful answers
If you have a very specific question you can also try All Experts and post a question to an expert there. I've done this before, there are some very helpful people. However, for what you are requesting, I believe google results will be able to answer your questions. Make sure you are using good googling technique. In this case, I would search for something like "Excel future value compound interest." See what you get and adjust from there.
