Stock websites I submit my photos to:

Shutterstock
Bigstockphoto
Dreamstime
123RF
iStockPhoto
Fotolia
Depositphotos

For starters, sign up to Depositphotos, Bigstockphoto, Dreamstime and 123RF - they have higher acceptance rate for photos and will help you understand how it all works. Shutterstock is the highest earner, but it's not easy to get accepted in the beginning. But don't let them deter you :-)