Itslawrence is 100% correct. The forum is easy to understand. Board has different sections. Each section has different topics. Each topic has different posts. These posts are separated by a light green strip like Itslawrence said.
For Example.
The Board Noobstown has sections like Town, Terraria and Trade. The trade section has topics like, buying, selling and exchanging. The buying topic may have posts like 'How much for eight pickaxes?' or 'I'll give you 15k for that diamond block.'
Sorry if it looks like I'm making you out to be a derp, but you did say you were confused.