Relays can be used by server admins to increase their server's view of the Fediverse.
To subscribe to a relay on Mastodon:
1. Log into your server’s website using your admin account
2. Go to Preferences > Administration > Relays
3. Click "Setup a Relay Connection"
4. Paste the URL of the relay into the box
5. Click "Save and Enable"
NOTE: General relays may overwhelm smaller servers. Hashtag-based relays tend to suit smaller servers better, more info at https://fedi.tips/using-relays-to-quickly-expand-a-servers-view-of-the-fediverse