QuickTime is a built-in -- but pretty basic -- option. There are plenty of third-party programs such as Camtasia, Screenflow, Profcast and many more (all paid software, though) with much more advanced features. If this is something you're going to do a lot of, you may want to make the investment.
As someone who has to suffer through a lot of TERRIBLE tutorials on YouTube, however, I beg you to look at the professional and highly-rated ones and then some of the others, and try REALLY HARD to be more like the best than the worst. Ye gods, the world doesn't need any more amateur-hour tutorials!!