From "Lexham Survey of Theology"

“Angels” are understood to be faithful ministers of God.
The Bible tells us that they worship God in heaven and carry out his assignments on earth. God commissions angels to protect his people, deliver them from danger, transmit divine messages, and encourage believers.

“Demons” are said to have rejected God and are in opposition to Him.
Their activities in the world are to engage in warfare with the angels (Dan 10:13; Rev 12:1–12), tempt people to sin (Eph 6:11), and deceive the world with lies that blind people to spiritual truth (1 Tim 4:1). Scripture also speaks of demons physically assaulting people and even possessing people to do their will (Mark 5:1–20).

“Satan”: According to Scripture, Satan was a particularly powerful and high-ranking angel who led one-third of the angelic host to rebel against God (Eph 2:2; Rev 12:1–12). Like the other angels and demons, Satan is an invisible being who is highly intelligent and very powerful. Since his initial rebellion, Satan has continued to work against God’s purposes in the world. He actively opposes the gospel by blinding unbelievers to its truth (2 Cor 4:4), persecuting the church (2 Cor 12:7; 1 Thess 2:17–18; Rev 2:10), and promoting false doctrine (Jn 8:44; cf 1 Tim 4:1). Satan actively seeks to influence and trap Christians in sin (2 Cor 11:3). Satan is also an accuser, calling the faith of Christians into question before God and accusing them. (Job 1:9–11; Rev 12:10)

“Spiritual warfare is the battle that continues between the armies of God and the forces of the devil. It is not poetry or play; it is real, and its plunder is the souls of free-willed human beings. If it were merely a matter of power, the Almighty God could master the prince of darkness in a moment. But because the ebb and flow of battle depends upon the will of humans – to receive or reject divine rule; to believe or refuse divine grace – the struggle for minds and bodies goes on. The adversary, who hates everything that even remotely bears God’s image, hates and seeks to control men."
- Jack Hayford