How does creating personas for marketing/design purposes differ from creating characters for fiction/drama, and how does one begin creating one?

In my design class, I have an assignment to create an interactive design while specifically thinking about the user audience. My teacher explained the importance of personas and the basics of creating one, and while I understand this in theory, creating a persona for my design has ended up being a little more challenging than I anticipated.

Now, I’ve done my share of writing and have created many, many characters for my stories before, so how do I translate my skills in character creation to making personas? Should I think of it as the same thing, or be thinking about something else while I create them?

I don’t know… it’s just a little confusing. Has anyone here had to make a persona before, and if so, could you give me some advice? Thank you. :)