To create a brand new WordPress.com site, you can go to My Site and click “create site” (if you have a brand new WordPress.com account) or the dropdown arrow to the right of your existing site list:
Then, click on the plus (+) sign on the top right corner of the screen
After that, select the option to either create a brand new WordPress.com site or add an existing WordPress.org (self-hosted) site. Please note you are not able to create a new Self-hosted site from the app. You would need to create the site from your hosting account and then you can add the site to the app.