Durood Sharif on Mohammad

Allah doing salla (DUA) to Mo. Q-Whom is Allah doing DUA and Salat. Who is real Allah and why he does DUA 
ALLAHUMMA SALLI ALA MUHAMMADIW
( Allah doing DUA to Mo )
ALLAHUMMA BAARIK ALA MUHAMMADIW( Barqat means blessing to mo)