Start by scoring the bottoms with an "X" and blanching them in order to remove their skins (25-30 seconds tops in the boiling water). Chop them roughly. You can remove the seeds or not. It's your choice. I don't.
Simmer them on the stove until the mixture reaches your desired consistency with a variety of add-ins depending on your preference (just tomatoes, tomatoes + marinara seasoning, tomatoes + chopped onions). Allow the sauce to cool and then freeze in Ziploc bags (I do 1-2 cup portions) for yummy tomato sauces. You can make tomato paste in a similar way.
When it comes time for use, I thaw it, pop it in the blender if it needs to be smoother, and use it for pizza sauce, pasta sauce, meatball sauce, chilli sauce.... All kinds of sauce!
Apparently... you can freeze a tomato whole. When it thaws, just squeeze it to remove the juice and then throw it in to whatever concoction you need it for... I've never tried this, but a few I know swear by it. Obviously they work better in a sauce or stew after this, as freezing does make them mushy.