Actually there are many way we have to do to earn bitcoin, but I will explain some.
*you can earn bitcoin from mining, this way But this way may be difficult because it requires a lot of capital to buy computer and hardware for mining. You will certainly get a large amount of bitcoin in this way.
*You can get bitcoins from sites that give free bitcoins to everyone, which needs to be done is to register and usually we can get bitcoins right away, but the numbers are small.
*We can get bitcoin by following a forum that discusses about bitcoin, and the resulting bitcoin is quite large.