Friends on Slopes work a bit differently than other social networks (by design!). Without public profiles, usernames, or anything like that, Slopes relies on you already being able to talk to your friend via some other service so you can send them a link. This goes a long way to avoid creepy strangers sliding into your DMs, bots, harassment, and more.
- Go to the Friends tab
- Tap on the + button in the top right of the screen
- Choose your preferred method to send the link to your friend
- Your friend taps on the link to open Slopes and confirm that they want to friend you