They resemble standard Daleks in appearence, but have black domes and instead of a sucker like arm they usually more advanced weaponary.
The Imperial Guard Daleks first appeared in Evil of the Daleks, where they served as generals and as the Dalek Emperor's personal guard. They were in charge of supressing the humanized Daleks. In the final stages of the revolt, the Emperor's Gurad tried to protect the Emperor in the control room. The humanized Daleks, convinced that all black domed Daleks were to be exterminiated, led the battle to the control room. Here the Imperial Guard was swarmed and the Emperor defeated. When the Dalek Emperor, who had survived the Time war, rebuilt his empire from the losing humans on board the game station, he quickly set up his own guards to protect him. They were given special features and markings to identify them from regular Daleks.
Like the rest of the other human converted Daleks, the Guard Daleks saw the Emperor as their God and feared the Doctor, the last Time Lord. They were eventually destroyed along with the rest of the rest of the Dalek Empire when Rose Tyler, a companion of the Doctor, absorbed the Time vortex and destroyed them all.