Introduction to the 2D World of Unity - Unity 2D Game Development - page 15

The orange-colored state is the default animation and the default state in the
animator tree. Right-click on the orange-colored PlayerIdleAnimation node in
the Animator tab and select Make Transition . This will attach the translation line
to the cursor. Move your cursor over PlayerWalkingAnimation and click on it to
drop it there. Now do the same thing, only in reverse—create a transition from
PlayerWalkingAnimation to PlayerIdleAnimation . Your animator node tree
should now look something like the following screenshot:
If you were to click on Play on the game now, you'll see that the animations play on
the Player object; however, it plays the idle animation, then immediately plays the
walk animation, then loops back to idle, and repeats ad nauseam. Almost there!