Rather than try to explain it, here's a good website complete with pictures and even a video!
http://www.taunton.com/finegardening...-tomatoes.aspx
Here's one more with some information about Heirloom Tomatoes
http://www.growing-tomato.com/Growin..._Tomatoes.html
Tomatoes are tricky. You have to keep them off the ground to keep them disease free and bug free. But if the plants get so fruit heavy, it's hard to do. I think both of these websites have some great tips for you!