The Bible doesn't answer all our questions about the devil -- but he (unlike God) is not all-powerful, nor can he gain victory over us when we are under God's protection. The Bible says, "He who dwells in the shelter of the Most High will rest in the shadow of the Almighty" (Psalm 91:1).
This isn't to downplay Satan's ability to interfere in our lives -- for he does have power, and sometimes his hand is very evident. I think, for example, of places that are torn by violence and conflict because of the schemes of evil men -- and I know that behind them is Satan. I know too that when we decide to leave God out of our lives and live for sin, then Satan is also at work. The Bible calls him "the spirit who is now at work in those who are disobedient" (Ephesians 2:2).
But never forgot two truths about Satan. First, he is absolutely opposed to God and His plans for our lives. His temptations may be very attractive -- but in the end they'll only harm us and lead us to death. Second, Satan is a defeated foe. By His death and resurrection Jesus Christ overcame death and Hell and Satan, and now we don't need to fear them if we know Christ.
Most of all, remember that we don't need to fight Satan and his temptations on our own. Christ is with us, and He will help us gain victory. Is your faith and trust in Him, both for your eternal salvation and for your life right now?