What is a challenge?

Question

I have seen the term challenge tossed around a lot on the boards, but what exactly is it and how can I win them for the sake of the "achievements?"

Answer 1

https://www.sololearn.com/discuss/123380/?ref=app

Answer 2

Thanks Frost, now I have the mobile app and already did two challenges :)
Can you do challenges on the website from a desktop computer?