Let’s see: Satan was originally an angel named Lucifer who rebelled against God. He was quite high up in rank (an archangel like Michael and Gabriel), and tried to set himself up as a being to be worshiped, and got one third of the other angels to follow him. God punished him by sending him to Hell, along with the other angels.
Later, when God created the universe, Satan somehow took the form of a snake and tempted Adam and Eve. Ever since then, he’s been going around tempting everyone, somehow. And rather than destroy him, God has decided to use him to test his people (cf. Job).
His motives are basically to get back at God, and he does so by trying to get people not to worship or follow God. He knows he can’t win, but his goal is to hurt God as much as possible. He does this by talking to us in our minds. He’s acts very similarly to the “evil conscience” you see in cartoons.
Oh, and he may not do most of those actions directly, but may rely on those fallen angels which are what we call demons. Or, demons and angels may be completely different things (as angels can’t possess people), and Satan and his angels are all still chained up in hell. I got a lot of conflicting information.
As for his destiny, it is as described in the Book of Revelation, where he is bound up for 1000 years after Jesus comes back, and is then released for a short time, and then finally thrown into the lake of fire, along with everything else that is evil. After that, he effectively ceases to exist.
I will also point out that, although I am still a Christian, my understanding has changed somewhat. I’m not sure if it is a good idea to get into the specifics.