The March 25th launch of Paper 2 is almost here... In addition to the game coming out, there will also be beta access to Steam Workshop features available from day 1!
The workshop will enable you to create and share your own levels (and paper visual designs) with other members of the community, and will be available with the game's release as a work-in-progress build to everyone who purchases the full game.
It's still a little rough around the edges, which is why it's releasing as a beta feature for now... In order to get access to the beta you have to opt into the correct branch and join the Steam group for the beta, as outlined here.
I am looking forward to seeing what you all create with these tools, as well as your continued feedback to help me shape them into something awesome!
-Bryce