Learn Arabic (Modern Standard): نحن نأكل سلطة، لكنهم يأكلون لحما. - We are eating salad, but they are eating meat.

You have learned that the conjunction و (and) attaches directly to the beginning of the next word. Similarly, the conjunction لكن (but) often attaches directly to pronouns. Here, لكن joins with the pronoun هم (they) to make لكنهم (but they).

Why does the word for meat (لحما) have an extra alif (ا) at the end, but salad (سلطة) does not?

Both words are the object of the verb (what is being eaten), so they both take an 'an' sound at the end. Usually, this requires adding an extra alif to hold that sound, as seen in لحما. However, words ending in a taa marbuta (ة), like سلطة, are strong enough to hold the sound without needing an extra alif.

How do the verbs نأكل and يأكلون show who is eating?

In Arabic, present tense verbs use specific letters to show who is doing the action. نأكل starts with نـ to mean 'we'. يأكلون starts with يـ and ends with ـون to mean 'they'.

Since نأكل already means 'we eat', do I have to use the word نحن (we) at the beginning?

No, it is optional! Because the verb itself tells us who is eating, you can leave نحن out. However, including it here adds emphasis to highlight the contrast between what 'we' are doing versus what 'they' are doing.