This are all the other buildings that aren’t defenses or for attacking. But they are equally important. The Town Hall is the centre of your village, the level it is decides which buildings you can have, how many and how far you can upgrade them. This also counts for the troops.
With the clan castle you can join a clan and house some extra troops that your clan members can donate. You can use this troops as extra for attacking or as defense.
With the decorations you can spice up your village, they don’t do anything in order of attacking or defensing but helps you customize the look of your village. The obstacles spawn random in your village, they cost gold or elixir to remove but give you gems back!