God created angels as He created all things for His purpose. The angels serve God and He has sent angels to people as blessings to help them and give them messages from Him. Satan used to be God's most beautiful angel until he thought that he could be like God and was kicked out of Heaven. In the Garden of Eden the serpent was satan, but it was a form that he took. In the Bible satan is depicted as that serpent, but he is not really a snake. If that makes sense.
So while God does give us, man/humans, domain over all of the animals we do not controle satan, truthfully he can controle us if we let him. However, as Christians we are given all that we need to resist the devil/satan. God gives us this power through His Spirit and Christ Jesus, if we have faith and truely follow Him then we can tell satan to leave us alone and he has to flee.
If you have any more questions feel free to PM me or keep posting here and I'm sure that someone else will be willing to answer you as well.