Open the Level Editor window using the Tools > Level Editor menu.
Click the + ****button to add a new level or select an existing one from the list.
Select the level theme, ground tiles color, and level ending prefab (use prefab Finish to use pre-made level ending). If you want to create a new theme, just follow the How to add a new theme guide. Required Precent - is the percentage of the items required to be collected in order to fully complete the level and move to the next one.
By clicking on object previews you can spawn objects on the scene and reposition them using default Unity Editor tools.
To test the level press the Test Level button or run the game while level is selected.