How do I get free gems?

If you get achievements, you can get free gems, for example, if you get to level 5, I think you get about 10 gems. However, I got 80 gems for defeating the elephant boss. If you don't know how to get on achievements, just go to where you open chests, click on the trophy, then it should pop up a bunch of achievements you can get or that you have completed.

P.S. this is how it was last time I played Idk if they changed it, also sorry it's a long answer...

You acheive acheivements

This is really easy. So, all you need to do is complete achievements and then press the tap that shows your avatar then go to the tap that says game then tap the trophy on the top