Learn Spanish (Spain): Comemos en el comedor.

In Spanish, the ending of the verb usually tells you who is doing the action. Because comemos ends in -emos, it can only mean "we eat". You can add nosotros (nosotros comemos) for emphasis, but it is usually left out.

Is there a connection between the words comemos and comedor?

Yes! They both come from the root verb comer (to eat). The ending -dor is often added to verbs to describe a place where an action happens, or a person who does it. So, a comedor is literally an "eating place".

Does the word en always mean "in"?

It means "in" here, but en is a very flexible preposition. Depending on the context, it can also mean "on" or "at". Here, because you are inside a room, "in" is the best translation.