It is easy to jump on the Web and search for just about anything. Just remember, that anyone can put anything on the Internet. Be a picky shopper when you are searching.
How do you know what is good? Part of that depends on what you need, but in general, if you look carefully at the site you should be able to determine: the source or author, the source's or author's credentials, when the information was created/updated, and why this information was created.
How do you find web sites? Most people use a search engine. If you are unfamiliar with searching, take a few minutes to go through one of the search engine tutorials - even if you are familiar with search engines you might find that you learn something new. Try the Google basic search tutorial -- http://www.google.com/help/basics.html .
Using the Advanced Search available on most search engines allows you to limit your search to domains more likely to have valuable information. Websites that end in .edu, .org, and .gov are educational, organizational or governmental and generally speaking are not trying to sell you something like a .com.
What about using Wikipedia?
Wikipedia can be very useful for for getting general background information to get you started and can even give you some clues on where where to look for more information by checking their bibliography. You may not use Wikipedia as a resource since you cannot assume that the author of the article is an expert.