Chaos is spot on, though for these sorts of questions you should check out the Jquery Documentation online - it really is quite comprehensive. The feature you are after is called 'jquery selectors'
Generally you do $('#ID').val()
- the .afterwards can do a number of things on the element that is returned from the selector. You can also select all of the elements on a certain class and do something to each of them. Check out the documentation for some good examples.