Learn Portuguese (Portugal): Eles abrem o supermercado hoje.

To conjugate regular -ir verbs for eles (they), you drop the -ir from the end of the dictionary form and add -em. This is why abrir becomes abrem.

How do you pronounce the -em ending in abrem?

It is a nasal sound, so it does not sound like the English word 'em'. Instead, it sounds quite similar to 'ãe' or the 'ai' in the English word 'paint' spoken through your nose.

Wait, do all regular verbs end in -em for eles?

Regular -er verbs share this exact same ending (like comem for 'they eat'). However, regular -ar verbs are different: their eles form ends in -am (like falam for 'they speak').

Why does the sentence use abrem instead of a phrase for 'are opening'?

The present simple tense (abrem) is perfect for facts, routines, or scheduled events like a supermarket's opening day. To say 'they are opening' right at this exact moment, you would use a different structure: estão a abrir.