Learn Arabic (Modern Standard): هذا البيت كبير.

In Arabic, there is no word for "is" or "are" in the present tense. You simply place the subject ("This house") and the descriptive word ("big") next to each other, and the "is" is automatically understood.

Why does the word for house (البيت) have the prefix for "the" (الـ) if the translation is just "This house"?

In Arabic, when you want to say "This specific thing," you must use the word for "this" followed by a noun with الـ (the). So, هذا البيت literally looks like "this the-house." If you drop the الـ and just say هذا بيت, the meaning completely changes to "This is a house."

Why doesn't the word for big (كبير) also get the الـ prefix?

Because it is giving us new information about the house, rather than just acting as an attached adjective. By keeping كبير indefinite (without الـ), it creates the "is big" part of the sentence. If you added الـ and wrote هذا البيت الكبير, it would no longer be a full sentence, but just an incomplete phrase meaning "This big house...".

If we were talking about a car instead of a house, would the other words change?

Yes! The word for house (البيت) is grammatically masculine, so it uses the masculine word for this (هذا) and the masculine word for big (كبير). If you used a feminine noun like a car (سيارة), you would have to use the feminine matching words, which would be هذه السيارة كبيرة.