In a large saucepan, heat the oil over medium-low heat. Add the garlic and sauté for 5 minutes, pressing the garlic down into the oil, until the garlic is light golden brown (adjust the heat if the garlic seems to be browning too quickly; it should just turn golden). Add the tomatoes, oregano, red pepper flakes (if using), salt, pepper, and sugar. Bring the sauce to a simmer over medium-high heat, then reduce the heat and continue to simmer the sauce for 20 minutes, stirring occasionally.
Serve tossed with the hot cooked pasta of your choice (spaghetti is the most popular pasta pairing for marinara!) perhaps topped with some freshly grated Parmesan, chopped fresh basil, or some additional red pepper flakes for sprinkling. Or use as a dipping sauce. If used as a dipping sauce, you can serve it either at room temperature or warm.
Notes
When sautéeing the garlic, stir frequently and press the cloves down into the oil, until the garlic is light golden brown. Adjust the heat if the garlic seems to be browning too quickly; it should just turn golden. If the heat is too high, it can quickly burn.
Serve pasta with marinara sauce with some freshly grated Parmesan, chopped fresh basil, and/or some additional red pepper flakes for sprinkling.
If you are using the marinara sauce as a dipping sauce, you can serve it either at room temperature or warm.