I've just done a thread about signing up at https://mstdn.social/@feditips/110923388035767741
You can import content from YouTube to PeerTube, either by manually reuploading the video files or automatically grabbing them from your YouTube channel.
Uploading manually gets you the best quality because it is the original, whereas importing from YouTube means it has been reprocessed/degraded by Google.
(The instructions for importing are at https://docs.joinpeertube.org/use/channel-sync)