How does bitcoin work? Who actually pays for the mining done?
You might want to read from actual recognised resources, beginning first at bitcoin.org. Various ways to explain how it works, from the basic picture probably most forum users even understand, to the highly technical that would only make sense to programmers. I generally introduce it just the way the white paper did.
Nobody pays for mining. It is completely voluntary - anyone can choose to mine, though because of today's difficulty and complexity, entry barriers are quite high (technologically and financially). Currently, though, miners earn a reward for finding new blocks ( 12.5 new bitcoins generated) and they keep the fees included in the transactions the include in those blocks. Thanks to demand and the appreciation of Bitcoin value, this has become quite profitable.