We believe that angels and demons really do exist. They are invisible, bodiless powers that inhabit the invisible realm.
Orthodox tradition holds that there are different types of angelic beings, for example, cherubim, seraphim, archangels and guardian angels, each with different roles and duties. Seraphim are described in the book of Isaiah as having 'six wings and many eyes', though this is symbolic.
Angels have free will, intelligence and are immortal.
Demons are the angels who have fallen into darkness. The highest among these is Lucifer, also known as Satan. We understand that demons are exceedingly cunning, and tempt us and try to pull us away from the truth.
So while demons tempt us and pull us to the dark side, angels would do the opposite. They are messengers and advocates for God. Orthodox Christian's believe each person is assigned a personal guardian angel. How they interact with us is a mystery.