Android apps: let’s clarify.
Sailfish OS is not Android, but an alternative OS descended from Meego Harmattan; fortunately it has a module (paid) to run Android apps.
This “Android-Support app” allows you to run apps in .apk format.
Whether it’s a mainstream Android app from Aptoide / Aurora, or whether it’s a FOSS app from F-Droid, you will need the License to run the app.
Visit shop.jolla.com to purchase one of the available licenses. The average price is usually around 49 euros, but Jolla makes discounts on some holidays during the year.
(At the moment it is not possible to buy license and phone together).
Native / “Pure” mode
If you already thought of staying Google-free, the basic version is fully working, with its native apps from Jolla Store and Openrepos.