Learn Portuguese (Portugal): Elas comem o peixe aqui.

comem is the 'they' form of the regular '-er' verb comer (to eat). To make this form, you drop the '-er' from the end of the dictionary form and add '-em'. Since the subject is Elas (they), we use comem.

Why does this sentence use Elas instead of Eles?

Elas specifically means 'they' for a group of females. If the group was all male, or a mix of males and females, you would use Eles.

How is the '-em' at the end of comem pronounced?

In Portuguese, an '-em' at the end of a word is a nasal sound. It does not sound like the 'em' in the English word 'them'. Instead, it sounds a bit like 'eng' or 'aim' spoken through your nose.

Can we say Elas comem peixe aqui without the o?

Yes, but it changes the meaning slightly. If you drop the o, it means 'They eat fish here' (fish in general). By keeping the o, it means 'They eat the fish here' (a specific fish or the fish that was mentioned before).