You can access the Beat Hazard workshop page here, or from the Ship Hangar in game. 'Subscribe' to a ship and it will be downloaded automatically and added to your hangar next time you run the game. Simply 'Unsubscribe' to remove the ship from your hangar.
Work-In-Progress and Finished Ships
Ships that are not yet final will appear with the text 'Work-In-Progress'. You can still subscribe to, and play with, these craft, however they will not yet have their own leader boards. Leader boards will be created for each ship once the final version of the ship is published by its creator. Final versions can no longer be edited.