To earn Bitcoin you have few ways. Mining own Bitcoin is the first way and secondly is revenue share sites. Revenue sharing site is very similar other sites which pay in the dollar for all your activity on that particular site.
You might know PTC and GPT sites which pay for completing the tasks.
Claim free bitcoin
Faucets are the best in making bitcoins in a legal way. You can find some running faucets in this blog posts. however, some are closed we still have good paying bitcoin faucets.
Few can be found here: Daily free cryptocurrencies
Just click the above link and claim bitcoins every hour.