The challenge is simple... Just go to steemit.com and sign up!
I'm still learning about the app, but it's an interesting concept.
My user name on challengeEOS is "ironshielder", yes that's ironshield with an er at the end. I had to make it 12 characters!
To install the app, just search challengeEOS in the app store and you'll find it. I did, it wasn't much of a... (Wait for it...) Challenge!
Have fun and be safe. Good night!