I use a foldable trellis to form my ring. Since the gaps are larger on it, I line the inside with burlap that gets tied on with twine to help keep the compost inside.
Then once folded and setup in the garden that already has the soil prepped, you simply add your compost. I've read that some folks just use compost with clippings & waste, then others also add 10-10-10 fertilizer and do lasagna layering. I've never added fertilizer to my rings since I had always assumed that the compost would be enough. Maybe the yield would be better if I added fertilizer too.
I've had success by adding a few feet of compost topped with soil. Then I dig a hole in the center of the soil which is where you water the plants (if it's really dry out, I'll also water plants directly). The compost will provide plenty of rich nutrients during the growing season and give you a bumper crop. The compost will also keep the soil more moist and hopefully prevent blossom end rot.
This year I only have Black Krim and Amish Paste tomatoes growing in my garden. Originally I was going to make more salsa, but my sister supplied me with a bunch of hot house tomatoes a few months back that yielded 45 pints of my husband's favorite snack. So I'm hoping that batch will keep him another year and free up my tomatoes for sauce and a few jars of stewed tomatoes.