The Adeptus Custodes form the Emperor's personal guard and are charged with serving and protecting the master of mankind. There are always several hundred warriors available in the Imperial Palace as well as a certain guards who never leave the Emperor's side.
Their armour and clothing are traditional, mirroring those of the first custodes. Their weapons look like spears, or spear-guns, but are actually spears with built in Lasers. These spears are also on their banners, badges and other regalia.
The guard never leave Terra and only rarely leave the Imperial Palace. Their place is at the Emperor's side.