Here is one simple recipe I use:
1 Tbsp olive oil
4 pounds ripe tomatoes, cored
Small yellow onion, finely diced
3 garlic cloves, minced
Salt and freshly ground pepper, to taste
2 tablespoons chopped fresh basil
Heat about a tablespoon of olive oil in a large skillet set over medium-high heat. Add the onion and cook until softened. Add the garlic and continue cooking until fragrant, about a minute more. Stir in tomatoes and their juices. Cook until sauce reaches a simmer, reduce heat to medium-low. Cook, stirring occasionally, until the tomatoes are tender, 20 to 25 minutes. Add salt and pepper as needed and stir in the basil.
Check out our Top 10 Ways to Enjoy Tomatoes.