Learn French: Nous mangeons du pain avec du beurre. - We are eating some bread with some butter.

In French, you can almost never leave a noun without an article like we do in English. Because you are eating an unspecified amount of a larger whole, you must use a partitive article (meaning 'some'). Since both pain (bread) and beurre (butter) are masculine words, you use du.

Do I always have to translate du as 'some'?

Not always! While the literal translation here is 'some bread with some butter', in natural English we usually just say 'We are eating bread with butter'. However, even if you drop 'some' in English, you still absolutely need to keep du in French.

Why is there an 'e' in mangeons? Doesn't the nous ending usually just add -ons?

Great catch! The verb is manger. If we just added the normal -ons ending, it would be spelled mangons. In French, a 'g' followed by an 'o' makes a hard 'g' sound (like in 'go'). To keep the soft 'g' sound from the original verb, we have to sneak in an 'e' before the 'o'.

What if we were eating a specific loaf of bread instead of just 'some' bread?