When first learning volleyball, most kids don't know what position they are and what that position does. As you get older, you learn to adapt to one of two volleyball positions and you'll always play that one spot. Especially if you're on a high school or club team because they're more competitive.
For the most part, the volleyball positions are either going to be setter, hitter or passer. Now for the more specific is for the hitters, you have the right-side (back), left-side, and middle hitters.
Your middle hitters are usually you're biggest player who should be able to block the best. Then you're right-side hitters or back players are usual left handed since it's easier for them to hit the ball on that side. Your left-side hitters can vary, but since right-side hitters are usual left handed, than they're usually right handed. Even though, there are back row hitters, for the most part teams don't use them that much.
Next you have a libero which is the player who always passes and doesn't play the front row. Finally, is the setter who just sets the ball to the different hitters.
Now for a volleyball courts' size, you should be able to land the volleyball in the court every time, right? Well many people can't, but when it does, the players need to be down and ready. The volleyball court dimensions make it easy to know where your position is.
The setter is usually center front row or some coaches have setters be right front row. However, there are some coaches that have the setters set from the back which I really don't understand. Then you have the libero who passes center back row every time they're in. Middle hitters are just hit middle and block all side, left-side hitters always hit and pass on the left side and then right-side hitters always hit back and pass right.
I know it may sound confusing, but you'll learn all of these positions sooner-or-later!