This site is a Q&A site where you can ask and answer questions. There are also a lot of other things you can do:

1. Vote questions up or down
2. Vote answers up or down
3. Accumulate reputation based on the questions you ask and answer
4. Edit answers, questions and tags (presuming you have enough reputation)

The idea is that a question and it's answer will improve over time and become a definitive answer to the question. So for example if you are asking what it the width of the Bottom Bracket on a Gary Fisher Superfly 100 the answer will be correct and can become 'the' answer to the question.

To have a look at how a successful knowledge exchange site works check out http://www.stackoverflow.com this was the first site of this type and if hugely successful amongst the software development community.

Have a look in the FAQ for some other information on how the site works (reputation, voting etc.).