You aren't getting enough water to it. The water powers the motion of the sprinkler and it has to be strong enough to force the switch to flip when it hits the bracket. This has happened to me many times.

Make sure your spigot is all the way open and you don't have anything else running water in the house. IF it still won't work, you can't use this style of sprinkler.

Does anyone know how to use these water lawn sprinklers... (see image)

My problem is that when it keeps turning, it gets to a point where it doesn't switch direction automatically. (I have to do it myself)

The sprinkler will go to one direction (completely), then it hits those black brackets to change direction. Once it changes direction to right, it will go up to some point and then stop; sometimes it stops halfway. I have to manually turn the sliver clip in order for the sprinkler to work.

How do I prevent this from happening?

****Forgive me as I am new to this!