Twine is an excellent tool for creating branching narratives. These narratives can be as simple as a choice based narratives a la Choose Your Own Adventure books. Twine also provides you a large assortment of tools that allow you to add both complexity and interactivity.
This comprehensive tutorial series aims to teach you Twine from the ground up. The series assumes you have no Twine experience or even coding experience. Follow along at your leisure.
Note: While you can jump around, the tutorials are meant to be followed in sequential order.