Learn Portuguese (Portugal): Cá em casa, o jantar é às sete.

Both mean "here", but cá is often used for a general area, like a country, city, or house. Aqui is usually for a more specific, exact spot. The phrase cá em casa is a very common expression for "here at home" or "at our place".

Why is it em casa and not na casa?

Just like in English where we say "at home" instead of "at the home", Portuguese uses em casa without the article a (the) when talking about someone's own home. If you said na casa, it would sound like you are talking about a specific physical building rather than "home".

Why does the sentence say o jantar instead of just jantar?

In Portuguese, nouns for meals like o jantar (dinner) or o almoço (lunch) almost always have the definite article in front of them. In English we just say "dinner is at seven", but in Portuguese you must literally say "the dinner is at seven".

Why do we use é (from the verb ser) instead of está for the dinner?

When we talk about the time or place a scheduled event happens, we use the verb ser (to be). The dinner is treated as an event on a schedule, so we use é.