Basically, it's an adjective which means providing detailed and practical advice about the way to do something. A how-to is an informal, often short, description of how to accomplish a specific task. A how-to is usually meant to help beginners, student or simply non-experts.
Everyone is busy in their lives, there are too many phases in which people face many problems and some of them are not that able to find their quick solution so they decide to take others help like they take help from their friends, family or even from the internet.
For example, if a guy wants to take a screenshot on his android phone but unluckily he does not know how to take a screenshot so he'll come out and search for the solution from any source. He could find the answer on the internet or from his friend.
In short, finding or providing detailed and practical advice about the way to do something is called how to.