Angels are created by God to serve and worship Him in Heaven (Heb 1:6-7).
Angels are very powerful (Ps 103:20) and above mankind in order (Ps 8:5) but are subjected to God as their Lord (all the “LORD of hosts” references in Scripture).
The Devil and demons are angels who rebelled against God (Eze 28:13-16). They currently rule over the world (Eph 2:2) but will be punished eternally in the Lake of Fire (Rev 20:10).
We are obliged to know what Scripture teaching about angels and demons, but need not fear them (Rom 8:38-39) and should not obsess with trying to know more about them (Col 2:18-19).