Welcome!
You will find a ton of information here that will really expand your knowledge of the world of mystery shopping. I suggest reading the "New Shoppers" area first and then start signing up with many, many companies. I'd start with the most discussed companies on the forum as they are all larger companies that operate nation-wide. Thereafter, there is a list linked at the bottom of the page with over 200 more - some of which are pretty small, but good companies, nonetheless.
Hard work builds character and homework is good for your soul.