What does it mean to comment on the first floor and the second floor?

The first floor, also called "sofa", refers to the first reply.

In the forum, there are usually many people attending. The landlord sent a main post to express the theme of the forum, and then invited friends to come in and talk. Host-the landlord will entertain guests, and of course there will be sofas and benches at home to entertain guests, but there are too many guests, so we should treat them equally. So the first person who arrives first (the first reply) can sit on the sofa, and the second one can only sit on the bench.

Second floor: also known as "bench", refers to the second reply.