You interact with PeerTube accounts the same way you interact with Mastodon:
You will only see videos that have been posted after someone on your instance followed that account.
To see all of the videos on a PeerTube account, click on the account's icon in Mastodon to open their PeerTube page.
For example, try going to the profile page for @yesterkitchen and click on their avatar picture, it should open their account on PeerTube. You will then see all of the videos they have published so far.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!