Angels have received horribly unfair treatment lately. They are portrayed as pastel sugar waifs and aliens. Some people even think that when you die you can become one - just read the Littlest Angel or listen to some Country music.
Actually, the angels were the first creation of God. They were given a free choice to serve God. Lucifer, in his pride (first among the capital sins), refused to serve and tried to take Heaven. St. Michael led the angels against him and cast Lucifer (Satan) and his followers into Hell.
The angels continue to serve God in many ways. They act as messengers like St. Gabriel. They serve as our Guardian angels. There are many other missions for the angels as well.