The Editor is how you develop any content in s&box.
To open the game in editor mode you can either append
-tools to your launch parameters or open
Tools can be accessed from the Tools main menu entry, or from the hotbar - these are all self explanatory for editing different asset types.
Add, create, enable/disable addons through the addon manager.
Every type of content is an addon; games, maps, etc.. creating new addons is as easy as pressing
Addons -> Create New... and following the dialog.
Different addon types can be selected from the dropdown.
You can inspect and modify entities or panels in your game at runtime through the inspector.