using version 2.79; I cannot identify any way to replicate the collections function in the outliner; it is therefore impossible to group the components of the rocket into a single asset. Here's what I show on my screen:
As an alternative, you can just select all of the objects you'd like to put together and press CTRL+J. This will join all of the separate rocket parts into a single mesh that you can use just like I use the collection instance in this course!
I definitely recommend switching over to Blender 2.80 soon though, so that you don't fall behind on anything!
Not quite, but it's SUPER close. They plan on pushing out the first Release Candidate (RC) on July 11th with a full release about a week or two later. It's definitely at the point of stable use though, so I'd recommend making the switch if you think you're ready. That way you can anticipate some of the changes :)