As you first start to play tennis, you will be taught how to properly "feed" the ball to get the rally going. Seems relatively simple. Usually, when you are feeding the ball to start your warm-up or practice sessions, you would bounce the ball then strike it. Remember, you will hit the ball in the point the same way as you feed it. However, a mistake a beginner/intermediate might make is to hit the "volley feed" the same way as a groundstroke feed. Essentially, this would cause you to swing at the volley, which is not advised.
When learning how to start the feed when you and your opponent are at the net, hold the continental (volley) grip. Try to keep your racket head up and slightly high (a little above your shoulder). Toss the ball up just a little and allow your racket to pull under the ball. This underspin or backspin will teach you how control the speedy ball coming at you. Also, by not having a follow through, you will be immediately ready for the next ball to come back over. As you get this perfected, try feeding a volley with your backhand. Set the racket up and back, toss the ball gently, not too high, then place the toss hand back on the throat of the racket and allow the racket to pull slightly under the ball. Again this action will teach you how to control spin and power later. You can practice this by yourself with a basket of balls. Place a target out on the court.
After reading this you can see why beginner/intermediate players make terrible decisions on low volleys as they are coming to the net or are in the mid-court. From feeding low to high all the time, they will swing and not control the low volleys. As they start feeding the "volley feed" high to low, they will start making better low volleys. Plus, you will be ready much sooner for the ball coming back, because you will have no backswing. This will help you look and play more professionally. Remember, bounce the ball on the groundstroke, but strike the "volley feed" in the air!
Good luck on the Courts!