You earn Bitcoin the same way you earn any other currency, by exchanging your labor, goods, or services for it. Figure out what you can offer of value to people and then do that but offer a discount if they pay in Bitcoin. Or you can simply buy Bitcoin outright using the currency you've already earned.
That said, here's some ways to facilitate earning Bitcoin:
--Freelancing
/r/jobs4bitcoins
Cryptogrind
XBTfreelancer
--Video Streaming
PopChest.com
Streamium.io
XOtika.tv NSFW
TheProtocol.TV
Watchmybit
--Social Media/Content Creation
ZapChain
Sato.sh
,...