Introduction to the 2D World of Unity - Unity 2D Game Development - page 9

A shiny new dialog box will open, which will allow you to tell Unity what each
individual sprite is within this sprite sheet. Like most things in Unity, this is pretty
easy—simply click and drag the cursor around each individual sprite. This will draw
a box around each one! As you do this, a little sprite popup will be displayed in the
bottom-right of the Sprite Editor window, which gives you some precision controls
on the position of the sprite and allows you to change the pivot. You may also click
on the Trim button to help trim the box of any unneeded empty space around the
sprite, which will trim the sprite down based on the transparency of the sprite.
As you draw out the position for each sprite, you will want to make sure the pivot
is set for the bottom each sprite. Another option would be to go to the Slice menu
(top left), leave Automatic as the Type option, change the pivot to Right, and click
on the slice button. Think of this like the origin point of the sprite—it will rotate
from this point, react from this point, and exist from this point. You will also
want to set the name of the sprites to something clear. Name the first 4 sprites
playerSprite_idle_01 , playerSprite_idle_02 , playerSprite_idle_03 ,
and playerSprite_idle_04 , and the final three sprites playerSprite_walk_01 ,
playerSprite_walk_02 , and playerSprite_walk_03 . With the sprites defined,
your Sprite Editor window should now look something like this:
When you are happy with how the sprite setup looks, click on the Apply button in
the top-right of the Sprite Editor window. You can also now close the Sprite Editor
tab. In the Project tab, you'll notice that playerSpriteSheet now has individual
sprites for each of the sprites you just set up! You now have a properly configured
sprite sheet to use in the project.