How can I teach the students a package/module in a computer lab? I will be teaching a course to college students in their 3rd year in college study.  So far, they have taken only one programming course in MATLAB. 

We have a package, i.e., is a set of functions, that simulate a certain task in our research field. It is written in MATLAB. 

We want to introduce the students to this package and make them know how to use the model without implementing the functions themselves. The students are 3rd year college students who took only one programming course in MATLAB.

I thought about setting up an example problem for the students to go through in the computer lab, run it and answer some questions. For example, calculate the mean of "x". What does the results in "y" mean? Are they realistic?

Is this the best method to teach such a computer lab? How do you teach well known packages, e.g., Akka, Spark, etc. in computer labs?
What you suggest is pretty typical for work in a lab. But I assume that you want them to know the package for a reason. You might tailor a few exercises that are related to that purpose so that it is an easy step for them from the lab to the intended use. 

It is also the sort of thing that might work well with pair programming if they need experience with that (they do, actually). Pairing will also free you up from answering simple questions that block students from forward movement while you only need to deal with more serious questions. Pairing is good in general for making everyone more productive. 

You can also save some time at the end for getting suggestions from students about how this package applies to their more general task. Just a check that they see the relevance.