First, the parts of the toilet, the handle, the chain, the flapper, the float cup and the fill valve.
Here's how it works:
When you push the handle it pulls on the chain, which raises the flapper and empties the water into the bowl. The water forces the contents of the bowl down into the drain pipe.
When the water empties from the thank it drops the float cup to the bottom and triggers the water supply. As the water fills the tank the float cup rises and when it reaches the top it turns the water off.
If the toilet is running you know that you need to check the float cup for leaks. If it won't flush you should check the chain or the flapper.
A little knowledge goes a long way!
