The two noun sentences, Ｎ1は Ｎ2です and Ｎ3は Ｎ4です, can be combined to form a single sentence by using で. Replace です at the end of the first sentence with で, and add on the second sentence, which remains unchanged.
ここは ゆうびんきょくです。あそこは ぎんこうです。
This is a post office. and that over there is a bank.
→ここは ゆうびんきょくで、あそこは ぎんこうです。
This is a post office, and that over there is a bank.