How to mark topic as SOLVED?

[Vegz78]

I see some topics are marked as solved and can find the category «solved» under my profile and «activity».

But I cannot figure out how to mark any of my own topics as solved or pick a post as a solution.

Is this not possible?

[randomuser]

For some reason I’ve only seen certain users be able to do it.

[PixelDoodle]

I don’t know how to auto set it. I guess it just happens when discourse assumes the topic a question.