Freenet's default feature is HTML sites - just like the regular web but fully hosted on Freenet and only accessible through it.

The content of those sites is whatever their authors want it to be :)

Further, dynamic applications such as forums are also available. Here's a list of apps built on top of Freenet: https://github.com/freenet/wiki/wiki/Projects

Freenet needs UDP so it likely won't work on Tails as Tails tunnels everything through Tor - which does not support UDP AFAIK.