The way you add friends changes depending on how far you've progressed in the game. The differences are as follows:
If you haven't recorded your first sleep session during the tutorial yet:
1. Press the "Friends" button on the screen with Snorlax.
2. To add a friend, press the person-shaped button in the top right.
If you've completed the tutorial:
1. Go to the Main Menu and select "Research Community".
2. To add a friend, press the person-shaped button in the upper right.
Additionally, players under 16 years of age cannot use the Research Community or the friend functions, so the respective buttons will not be shown.
*Age restrictions may vary depending on your location.