If you've already used the simulation deck, it should be pretty straightforward. Here a few tips:
You'll notice there's a new "Browse Workshop" button on the Simulation screen in the Omni UI (tab menu) on the simulation deck. While browsing, if you see something you like, just click the Subscribe button and it'll be downloaded into the game. The same applies even if you're just browsing in a web browser outside of the game: anything you subscribe to will be downloaded for you in the game.
When you've created something you would like to share, click the new Publish Current Pattern button. You'll get a progress bar, and then it'll open up the Workshop page for your new item so you can edit its attributes if you want.
One other thing that's fixed here is a potential crash while in the simulation deck. Special thanks to dasrobse for reporting the bug!
There is one known issue with the simulation deck in the current build: if you exit the game while on the simulation deck, the next time you come back, the Omni UI might be sideways. If this happens to you, open the Omni UI, then move backwards a little bit so you can see more of it. Maneuver your cursor so that you can click the Simulation screen button (up/down will move it left/right, and vice versa). Once on the Simulation screen, click the Exit Simulation button, which will take you to the main level. Exit the game, then open it back up and you'll be good to go. Alternatively, you could hold Left Alt + Right Shift, and type IVEFALLENANDICANTGETUP. If done correctly, it will appear to freeze the game. Just hit the Esc key to get to the main menu and exit the game. Re-launch the game and you'll be good to go.