Here's the thing I need to confess though. I use canned tomatoes. So for me to make my own, I am really just adding a bunch of ready made ingredients together for the most part. It feels like cheating, but it tastes really good. Maybe one day when I have more time on my hands I'll be able to use fresh tomatoes, but until then canned tomatoes are working just fine.
There are many, many different recipes out there. You can even just wing it and add stuff by taste if that is your thing. There is no wrong way to make it. I make it a very simple way. Here's what I use and how I do it.
Add some chopped onion and garlic with olive oil to your pot. (I enjoy making it in my Le Creuset, and it is super easy to clean up afterwards.)
I use a can of tomato sauce, a small can of tomato paste, and a can of diced tomatoes. For the diced tomatoes I like the Italian seasoned kind with basil and oregano. I buy whatever is on sale or the best deal. I mix and match brands, and it tastes fine like that to me.
Add the diced tomatoes and stir.