Usage

To use the toilet first sit on it, then you can press the keybinding (U by default) to use it. After you are done you can leave it with shift as with a chair, and then you can flush it by clicking on it with an empty hand. However it needs water to function, a water source a block under the floor will supply it with what it needs. Alternatively a water bottle and bucket will suffice.

There is also toilet paper, but which is the correct orientation?! (Shift left click on it to flip it)

Crafting

The toilet can be crafted with quartz, a bucket, and a button. To craft toilet paper you need 1 stone and 8 paper.