Know-how is the knowledge and skill needed to complete a task. Mechanics have a lot of know-how when it comes to cars.
This folksy word pretty much defines itself: when you have know-how, you know how to do something. People pick up know-how in many ways. In school, you can gain know-how, especially in classes that are very practical. The best way to get know-how is through experience. For example, teachers may learn about teaching in school, but they won't have a lot of know-how till they've spent a few years in front of a class of students.