To add a persona to a project,
Open up the project to which you want to add a new persona.
Click on the ADD NEW button on the project page.

You'll see a pop-up window in which you need to select Persona. Select either a blank persona or one of the suggested templates.
Hit ADD, and here you go — a new persona appears in the project.

To start editing your new persona, click on this persona's name and it'll open in the Persona Editor!
Learn more about creating effective data-based personas at UXPressia Academy.