Okay, tomato sauce, in a rambling sort of way!
Tomato sauce can be literally just that: sauce made from tomatoes, only. Most people don't consider this to be an acceptable sauce, though, and store-bought sauces can contain an astounding array of ingredients and fillers, sweeteners and thickeners, etc. I don't know what type your tastes run to to, but I find personally that sugar's rarely if ever -needed- for a decent homemade tomato sauce.
All tomatoes are not created equal, too; the reason Roma tomatoes are typically used for sauce is that they are a fairly dense, 'dry' tomato; they should not be watery. The downside is that Romas are often, as tomatoes go, and with modern plant-breeding, rather bland despite having a medium-high acidity. I think I remember you saying you had lots of Roma tomatoes for your sauce, but I'll give you a basic recipe that you can use with almost any tomato type - I'm also assuming you're going to want to make a large batch and freeze it later. Keep in mind that in my experience, ANY tomato sauce recipe just about can have its flavour punched up later through some tips I'll go into later, so it's okay to start with a bland recipe and experiment or improvise from there. (I know someone who swore by adding Pernod to tomato sauce, for instance.)
Many recipes will tell you to peel the tomatoes before use. I will give you instructions on how to do this relatively easily if you don't know, but I will also note that I don't find it necessary. I -do- cut off the stem scar (the dry, ridged bit on top where the tomato had been attached to the stem) for reasons of taste and also health concern(a), but the rest of the tomato goes into the pot with me.
5lb tomatoes, loosely chopped
1 to 2 cups water (1)
1/4 teaspoon salt
3/4 to 1 cup finely minced onion, garlic, parsley (2)
1/2 teaspoon ground pepper (3)
1 tablespoon olive oil
dollop of oil
other to taste (b)
enameled stockpot, at least 6qt capacity (4)
measuring spoons & cup
As always, wash your vegetables first. Chop your tomatoes into reasonable chunks (length should not be longer than from your fingertip to your middle knuckle of your index finger and width shouldn't be much bigger than your finger-width; smaller is acceptable, but this is not something where precision matters). Pour the pieces into your pot; add your water, salt, pepper. Turn onto low heat.
Prepare your onion, parsley and garlic. Garlic and onion should be peeled and minced fine to medium-fine (again, precision isn't very relevant here, but it should be in lots of pieces). Heat dollop of oil in pan over low to medium and add onion and garlic. Sautee until soft, what cookbooks often call translucent. Try to keep from browning; if it looks like it will brown, lower the heat. Add to pot. Parsley should be minced quite fine and added at this time along with remaining olive oil.
Raise heat to medium and stir thoroughly, focusing on the bottom, every so often (5) to keep the bottom from scorching. If it seems likely to scorch, again, lower the heat. Allow it to reduce (it WILL reduce) over the next couple of hours and thicken. If it seems to show no sign of thickening on its own and you're running out of time, you can resort to a few different options; cornstarch, a cooked potato, mashed up, flour, etc. A favourite is often instant mashed potato flakes, but I've known people to use anything, including oatmeal.
Tomato sauce thus prepared will keep in the fridge for up to 4 or 5 days, and can be frozen and used indefinitely (probably not more than a couple of months for best results).
(a) - recent FDA studies have suggested, not proven conclusively, that the hepatitis virus sometimes transmitted through vegetables is, in tomatoes, stored in the stem scar and that the rest of the tomato seems proof against it. As it's far from conclusive, I wouldn't bet my lunch or my life on it - but cutting the stem scar out, it's the bit at the top of the 'core' from the skin down to where the seeds begin - that whitish 'plug' - is easy and fast, and a small enough chunk of tomato that I don't consider it wasteful.
(b) - there is seemingly no real limit to what can be added to tomato sauce. Carrots, celery, chicken, beef, flour, corn... it's between you and your tastebuds, ultimately. I can give guidelines on these, or you can just experiment, or ask questions if you have 'em, but as this is for a 'base' recipe which can in and of itself be modified, I have eschewed them in here. If you are sold on oregano and basil, though, this is where you add them - I'd say about a teaspoon each, or one tablespoon of Italian seasoning as sold by the stores.
(1) - water is NOT the only liquid you can use in this. Just about any 'edible' liquid can, though I recommend non-basic liquids; no milk or cream (though those can be used in such recipes sometimes too). Recommendations: water, wine (red, white, or any really, although advisedly grape wines and not other fruit wines), stock or broth; harder liquors should be used more sparingly and as flavouring agents primarily. You usually will not use more than 1 cup of stock or broth because of the fats in it, unless it's vegetable broth.
(2) - Proportion is a matter of taste - as is amount. This is a basic recipe to start with, though, and it would probably be at 1 cup, about 1/2 cup + 2 tablespoons of onion, 1/4 cup parsley, and the rest garlic. But if you're not a big fan of onion and you love garlic, you might cut the onion down and up the parsley; or you might hate parsley and do away with it altogether; etc. It's one of those areas where 'it depends'. If you hate any of this trio, let me know and I'll work out a substitution with you. For onion type, I usually use sweet onions or yellow onions; if you use white onion you may want to cut back a little on the amount as they are stronger.
(3) - pepper type is also up to you. I have used cayenne, black, green, white; I've substituted paprika at times; etc. Usually I tend to use a lot of pepper, but this amount's a good baseline for most people's tastes.
(4) - you want your stockpot to be enameled, and not unenameled aluminum or the like, because of the acidity in tomatos and tomato sauce. Cooking tomatoes in an unenameled aluminum pot will often result in an aluminum taste creeping into your sauce. Enameled pots are proof against this. You also don't want to cook them in unenameled cast iron for the same reason (and because it can screw up the cast iron pot!). You also want a wooden spoon and not a metal one, not for this reason so much (for whatever reason, metal spoons are more often nonreactive, I don't know why) but because the clanging of a metal spoon on a metal pot will drive you nuts - especially if you have a headache.
(5) - the first few times you make this, try to stir it every 10-15 minutes until you get familiar with your stove and pot to figure out what temperature is perfect to allow it to cook without scorching. As you get used to it, you'll get better at knowing how long you can safely walk away for before you need to attend to it again. When I make it, I check on it every half hour or so and otherwise do other things.