All of your ships are held in the Ship Hangar. Select the hangar from the main menu to see the details of each ship. Each ship can have up to four missions to complete. Simply click on a mission to attempt it. Where relevant, that game will show you a list of valid tracks to use and will temporally alter your perks and the game settings to meet the mission criteria.
Creating a New Ship
Select 'Create New Ship' from the Hangar menu to start work on your own creation. The game will create a 'test' ship for you which you can then edit. Each of the ships attributes can be altered by selecting the appropriate tab at the top of the screen. Use the mouse wheel to alter the settings in each of the menus.
The basic settings contain all attributes that cost 'Edit points'. These settings are the ones that will determine how your ship will handle and fire. Each setting will add or take away from your overall 'Edit Points'. Your Edit Points must be zero or higher for your ship to be valid. Attributes have different weightings so you need to experiment on how best to balance your ship.
Creating a Ship Image
You will need to create a .png file no bigger than 256x256 pixels that will represent the image of the ship in game. Here is an example below that I quickly threw together using the Beat Hazard 2 ship pack:
Here is a zip file with ships, and ship parts, to help get you started:
PNG images are needed in the game as they contain alpha information, that is to say parts of the image can be transparent. You can use a paint program like Photoshop to create a .PNG image. Or you can download a free art program like gimp
Testing Your Ship
You can test your ship at any time from within the editor. This will drop you into chill-out mode with infinite lives.
Publishing Your Ship
If your ship is finished, you can publish the final version. This will upload the craft to the Steam Workshop and then lock the ship so you can no longer edit it. If you are still working on your ship, you can publish a 'work in progress' version. Other players can download and test it, and you can continue editing it at a later time. Note: Work In Progress ships will not submit scores to any leaderbaords.
You can edit this on the Steam Workshop page.
Advanced mode allows you to create asymmetric ships. In this mode you can have turrets and engines that are not lined up with each other.
I hope you have fun creating your own ships, I can't wait to see them!