What is it?
Storytelling is a type of activity in our daily lifes for sharing experiences, explaining values etc. You can take advantage of storytelling by forming your own stories as well as listening to users' stories in order to empathize.
How can I use it?
First you need a domain and persona for your story. Throughout the story, the persona tries to deal with the issues in the domain. Also you have to settle the flow and phases of your story. You need to define the main problem of the story which is close to the middle of the story. Likewise you can need some minor problems during your story.
When can I use it?
In early stages you can use it on the purpose of problem framing. Also you can use it for solution framing. As a designer you can use it to both get insight to users and pull your team to the same spot in terms of empathy with the user.