I think you've missed something in the tutorial.
The way animation works is that it's triggered by some action, generally for platformers you'd be looking at an entry such as "On key down (Right key) play animation "walking"".
Then the same with a "mirrored" for left movement and a "standing" animation for when the "player is not moving".
The above isn't quite correct, it's just an outline, so I've added to your capx so you can see what's required;
dropbox.com/s/wxex3ipip5ekfj7/Myfirstproject.capx
You'll see the entry for the Right key has a "not mirrored" addition to it, without this, once you've moved left you remain facing left even when moving right.
You can play with the settings in C2 by disabling individual actions (right click) to see the effects.