In Clash of Clans the buildings are split into four categories:- Resources, Army, Defenses and Decorations.
Broadly speaking your Resource buildings allow you to generate and store Elixir, Gold and Dark Elixir. Your Army buildings allow you to train troops, research new troops and learn new spells. Your Defense buildings provide protection for your town.
Here you will find details of the resources needed, time taken to upgrade, and the bonuses for each level of your buildings in Clash of Clans.