Flushing is displacing the content of the bowl down the drain. This is usually done by releasing a volume of water at once, which is a rate of flow higher than what your water line allows, hence you have to store a volume of water somewhere in order to release it at once (flushing).<p>You can, for example, fill a bucket of water then releasing that water into the bowl to flush its content, but more practically, that water is stored in the cistern/tank that comes with the toilet or that you can purchase separately.<p>Your water pipe supplies that cistern with water, but there must be a way to stop the water when the cistern/tank fills up or it would overflow and flood your bathroom.<p>So, you need to control the process of water filling up your cistern and, in order to control something, you must first measure it. In other words, there must be a way to know the level of water in the cistern to prevent it from overflowing. This is usually done with a floater inside the cistern, which floats on the water surface.<p>Now that there's a way to know the water level, there must be a way to act upon that information and stop the inflow of water when the water gets to a certain level, or as we have it now, when the <i>floater</i> gets to a certain level.<p>This is usually done with a coupling mechanism that ties the floater to a sort of valve. The water level rises, the floater rises with it, and this force closes the valve that's letting the water in the cistern/tank. The water then stops. You have a full cistern/tank.<p>Now there must be a mechanism to release that water all at once from a hole at the bottom of the cistern/tank. This is what happens when you "flush" by pressing on a button or pulling down a lever or something. The water goes down all at once and the cistern empties. The water level goes down, the floater goes down with it, and there is no force closing the inflow anymore given that the floater is down, so the cistern starts filling up again...<p>But, you have a hole down there... Which means that something needed to be closed down there in order for the cistern to fill in the first place and you need it now to fill it again... This is a "flapper". This is usually a membrane of sort that closes the hole in the cistern at rest, but that gets "lifted" when you action a the "flushing" lever or press the button in order to let the water into the bowl.<p>So, water goes in, floater rises and reaches a certain level, that water pushing the floater is a force that closes the inflow, and the tank is full. You pull down a lever or push a button to flush, the flapper is moved and reveals a hole down the cistern from where the water goes out all at once. The water level goes down and so does the floater, there's no force closing the inflow and the cistern starts filling up again.<p>Happy to answer questions.