There are many different ways one can earn bitcoin.
But i want to mention this three ways for now. Bitcoin can be buying and selling as other currency is being done in the fprex.
One can be earning bitcoin like in this forum or a little pick from the bitcoin faucet.
Faucets are really useless, I am not even sure why people even consider this as a way of earning. First off, it gives you shit amount of satoshis. Then you have to deal with transaction cost for miner's fees, then you would realize that it isn't even enough for paying your electricity and interenet bill.