The answer to your question can get quite involved. When you go to that website, go to the spot that gives you explanations of all the different SEC filings. Also, yahoo and Hoovers can get you into SEC filings if your broker does not provide Edgar access.
Suggest you start with the 10K which is year end filing and the 10Q which is the quarterly filing for any company. They will give you financial information (fundamentals) as well as other meaningful data about the company. Then look at some of the other filings such as an 8K or an S3 to see what the differences are and how other filings may be of help in making trading decisions.