Peel them, crush them up, heat while adding spices, simmer until it can coat the back of a spoon without sliding off.

For a better sauce, begin sauteeing onion in butter or olive oil until fragrant, add garlic, also cook until fragrant. If making meat sauce, brown the meat with the onions and garlic at this time. Drain the fat, then start adding and crushing the tomato, as well as your spices.