For those who want to just experiment with bitcoin - without actually investing money (because you don't need to) - signing up for Earn.com would be a great exercise.
"I Don't Buy Bitcoin, I Earn It." - Andreas Antonopoulos
Click this link to go to Earn.com:
earn.com/rafpadilla/referral/?a=piq9nrjxzh0ocxfy
I searched the app they have on the app store and it's got a decent handful of downvotes.