Learn Italian: Mangio la pasta con la salsa. - I eat the pasta with the sauce.

In Italian, many prepositions combine with definite articles to form one word (like di plus la becomes della). However, the preposition con usually stays separate in modern Italian. You might see the combined form colla in older texts or hear it in some regions, but writing con la is the standard rule today.

Would the sentence change if I just meant eating pasta with sauce in general?

No, it would look exactly the same! In Italian, you almost always need the definite article (like la) before a noun, even when talking about general categories or uncountable things like pasta and sauce.

Could I use il sugo instead of la salsa here?

Yes, and it might even be more common depending on the dish! Salsa usually refers to a smooth, raw, or lightly cooked puree. Sugo specifically refers to a richer, cooked pasta sauce, often with chunks of meat or vegetables.