Although your entire team rotates on every play, there are some positions in volleyball that you should know about.
This player hits from the strong corner. What do I mean by that? If you're right handed, the strong corner is front-left. Lefties come from the front-right corner to be most powerful.
Usually a very tall member of the team. Plays mostly in middle front and blocks every hit. Will usually move to form a double block with either outside hitters.
Main responsibility is to set up the hitters--wherever they may be (this could even mean back row). The second contact of each possession is meant for the setter, but if he/she can't get it, he/she must yell 'help.' If for some reason the setter must touch the first contact in a possessoin, he/she should cry 'setter out' to let your teammates know that the setter cannot get the second ball.
These two positions are not one and the same, but the descriptions for each are very similar. Defensive specialists only play in the back row, but if they want to come in the game, they must make a substitution with the referees. Liberos only play back row, but they are allowed to go in and out the game as much as they need. Bookkeepers usually have a tracking sheet for the libero. Liberos must wear a different jersey than the rest of the team to differentiate between them and the rest of the team. They do a lot of rolling and digging to keep the ball in play!