This is a quick guide on how to play the game if you don't have a gamepad and you're only using controls!
These controls are also shown in the introduction tutorial that's shown in the story mode, but for those that still aren't sure how the controls work, they go like this:

When you go up to serve, you have two choices:
X: Overhand Serve (Jump Serve)
Z: Jump Floater Serve

Overhand Serve: Hold X until a yellow ring forms. When the ring is done forming, a trajectory line will form. Hold down X until you see the trajectory go the way you want it to. Next, let go of X so that your character tosses the ball in the air. Finally, Hit the 'Z' button the FIRST time to jump and 'Z' the SECOND TIME to actually hit the ball!

Jump Floater Serve: Hold the 'Z' button the whole time until your character and the ball are both in the air. Let go of the 'Z' button when the ball reaches chest level to serve the ball in. It works most times, it depends on the timing and how far away you start your character.

When the setter sets the ball for you to attack, you can do the following:

Spike: Press 'Z' the first time to jump. Try to jump close to the center of the ball so your character can line up with it better, or get your character just behind the ball. Press 'Z' the second time to actually spike the ball, it will go in a downward trajectory really fast.

Roll Shot: Press 'Z' the first time to jump, then instead of pressing the 'Z' button again, press the 'C' button while in the air to do a roll shot.

Tip: Practice doing these two shots in the spiking training in the game. Roll shots seem the most effective if the opponent's block is timed perfectly to your jump and you can't spike through the block. You can roll shot over the block to have a long rally, and either set up for another attack or block their shot!

To block, there's only one button to use:

Up Arrow: Hold down the up arrow on the net to adjust the height of the jump.

Tip: The less time you push down the up arrow, the lower the jump. The longer you hold it, the higher the jump. However, your maximum jump height is determined by your jump stat, so upgrade it to jump higher.

There are two ways to defend the ball:

C: Diving saves that save any ball in the nearby area. If it's off the block and you need to chase a ball far away, the 'C' button can make you dive great lengths to save a ball and keep the ball in the air and in play.

Tip: This move doesn't lose your defense shield, so you can use it if your defense is low and works very well!

Down Arrow: Proper receiving is done by moving your character to a spot where an attack might occur. When the opponent is about to do the attack animation, press the 'Down Arrow' to receive the ball.

Tip: This button doesn't have to be pressed immediately when the ball is at you, it can be pressed a little earlier, and it gives you more time to decide where to place yourself for the dig.

If there is anything I missed, please let me know! I hope this guide gives you a basic idea on what buttons do what, and helps you win games that you may struggle on!