Angels are spiritual beings who were created by God to do His will, but some of them (including Satan) rebelled against God and became evil. In that sense, therefore, some angels are bad (although the Bible usually refers to them as demons, not angels).
Satan didn't create any angels; only God had that power. But Satan did trick some of them into rebelling against God and becoming his followers, claiming he was more powerful than God and would take God's place as the ruler of the universe. They believed him, and since then, Satan has used them to do his will. Satan's pride persuaded them: "I will ascend to heaven; I will raise my throne above the stars of God.... I will make myself like the Most High" (Isaiah 14:13-14).
But Satan's promise was a lie, as are all of his promises. His rebellion failed, and Satan is now a defeated foe! How do we know this? We know it because by Jesus Christ's death and resurrection He overcame Satan's power over sin, death and hell. Someday Satan's defeat will be complete, and he will be banished forever "into the eternal fire prepared for the devil and his angels" (Matthew 25:41).
In the meantime, however, the devil and his forces are still at work, seeking to turn people away from God. Don't let this happen to you, but make sure of your commitment to Christ. The Bible says, "Resist the devil, and he will flee from you. Come near to God and he will come near to you" (James 4:7-8).