You can either use the "Search this board" function to the right of each board name, or the site search, on the top left of the site. This link gives more of an explanation of the search options:
There are different defaults in terms of result order and time frame in those two search options, but you can always change the parameters. By "how to ask questions" - are you referring to posting, or something else?
As a first pass, I'm going to refer you to our FAQ: http://www.chow.com/faq
It covers 'How do I post a new topic to Chowhound?' as well as 'How do I search for something?'
If you still have issues after you read the FAQ, please post back here, and I'll try to explain in more detail.