How challenges work

Question

I have been seeing people complete challenges lately but i don't know how to go about it, do i just have to select any random person without their permission or do i have to message the person about it?

Answer 1

You don't need to message him.
You should choose random person then challenge them.
If they are interested they will accept it otherwise they will decline it.
You can also challenge a specified person by visiting his profile clicking challenge.

Answer 2

You're free to challenge anyone anytime, but the person you're challenging can either accept or decline the challenge if he wants.