Who are angels?

Angels are Allah's creation. They are made from light. They can change into the shape of a human. In surah Marium, angle Gibrail appeared before her in human form. In a hadees it was narrated that angel Gibrail came to our beloved prophet صلی اللہ علیہ وسلم in the shape of Sahabi from Syria called Dihya Al kalbi رضي الله عنه

Angels are neither male nor female, they don't marry and don't have Children, they don't eat nor drink and they do not sleep. They don't have any authority to commit any sin. They are innocent and they don't sin even under influence or force. Their only propose is to fulfill Allah's instructions. They do not forget their duties or instructions.
To insult an angle is kufr.
Angles are each given a particular job.

To do wahi,

To blow the horn,

To remove the soul,

To do tawaf,

To write amal,

To ask questions in the grave,

some remain in the position of kayam, others in Ruku, our Sajda.
When we sleep an angle comes and sits near our head and makes sure no insects or animal should enter our nose or mouth to choke us.
If a Muslim does wuzu and sleeps angles gather around him while he is asleep.