Libero is the defense specialist, the person who recieves the ball in the middle. Covers deep hits and is a back up setter.
Outside Hitter is the main attacket on the team. Playing on the left side of the court, outside hitter is the position that spikes, and gets sets from the setter. There are usually two outside hitters on the court.
Setter is the ball handler. This position is the one that usually gets second touch. This is where most plays are made. The setter has multiple options to set the ball, Outside, Middle, Pike, Opposite, etc.
Middle is the tallest position to play. This position is the main blocker of the team, being tall and able to attack. This position is one of the funnest to play, as you get to be around the court.
Opposite is the person that attacks on the right side of the court. Usually behind the setter, opposite gets the back sets of the setter, as a surprise attack. Opposite can also set the ball if the main setter gets first first touch.