PeerTube federates with the rest of the Fediverse, so you can follow PeerTube accounts from Mastodon etc and share videos, comment on them, like them etc too.
Here's an example account you can follow: @craftykat
PeerTube works in a really clever way: if lots of people watch the same video at the same time, they transmit the video to each other by peer-to-peer. This means even if a video goes viral, the PeerTube site that hosts it doesn't crash. Even small sites can provide videos for a large audience.