There is no specific content type required, you are free to create whatever you think.

There is no specific type, subject or topic to follow, you’re free to create whatever you think would be useful to our users. Your file must be original that owned by you & editable resource except photos or jpg background. Please check out the “Item types available on Freepiker” article in Technical Issues section at Help Center to learn specific item types those are currently available on our library.