It's actually a pretty easy process, but not for the timid since it takes a great deal of time and a lot of tomatos for very little return.
For truly sun drying, good hot weather with lots of sun are an absolute requirement. Any tomatos will do, but I find Romas to be the best since they have fewer seeds than others. Cut the stem end off and throw it away... halve the tomatos length wise and place on a rack of any kind. I happen to have an unused window screen in a wooden frame about 3 feet by five feet in size. I place the tomatos cut side up, cover with cheese cloth (to keep the bugs off)... the cheese cloth shouldn't rest on the tomatos (I stuck a few sharpened pencils, point down into the screen to hold the cheese cloth up). I bring them in at night.
It'll take anywhere between a week and three, maybe even four weeks, depending on your weather.
10 to 12, 4 inch tomatos will produce about an ounce and a half of dried tomatos, however the taste is highly concentrated.
We lightly salt ours, just a tiny bit of pepper and a sprinkle of fresh basil from the garden. Suit yourself.
If you don't want to invest the time, you can do it in a 200degree F (100 C) oven in about a day or so... same process though.
Best of luck!