Learn Portuguese (Portugal): A mobília da sala é nova.

In Portuguese, a mobília refers to a complete set of furniture for a room or house. It does have a plural, as mobílias, used when talking about multiple distinct sets. If you want to talk about individual pieces of furniture, you usually use the masculine noun o móvel (plural: os móveis).

Why is it da sala instead of just saying the Portuguese words for living-room furniture?

English often stacks nouns together, like living-room furniture. Portuguese does not do this. You have to link the nouns using de (of). Here, de merges with a (the) to make da, so the sentence literally translates to the furniture of the living room.

Does sala always mean living room? I thought it just meant room.

While sala can mean a large room for a specific purpose (like sala de aula for classroom), when talking about a house, it is the standard word for the living room. The full name is a sala de estar, but it is almost always shortened to just a sala. A bedroom is a different word: o quarto.

Why do we use é (from the verb ser) instead of está? The furniture will eventually get old, so isn't being new temporary?