Loop_out is not defined

Your syntax is wrong. If you are using the latest versions of After Effects you should get an auto complete.

The proper format for a simplified loop out looks like this:

loopOut()

Cycle is the default so it is not necessary to enter anything if you want to cycle. the second value counts the number of keyframes backward from the last keyframe to set the loop start and end. Zero is also the default and that means all keyframes will loop. 

The other options for the kind of loop you want to perform are:

"pingpong"

"offset"

"continue"

Please check out the expression language reference by typing loopOut or any other expression operator, or just expressions in the search help field in the top right corner of After Effects. That will take you here and you will find a description of how loop works about halfway down the page.

If something is not working for you in After Effects the first resource you should use is the Search Help field right there in the top right-hand corner of AE.

I am also curious about the training you are using. If it was high-quality training you never should have made the syntax error. Please post a link. I think the best place for a new user to start is the User Guide. You should also check that out.