Can I use a font in a website, app, or eBook?

Depending on a license you buy the font with.

Creative Market only has one license and it doesn’t cover web-fonts, applications or eBooks. If you need one of this licenses, I would advice purchasing them on one of the following websites: Fontspring.com, Fonts.com, Linotype.com, MyFonts.com.

Usually eBook license covers 1 title but multiple copies.