including a class in a Java file in a project

I am probably putting this in the wrong place but I need some help. I apologize in advance if this is something easy, but I am not a java programmer or very conversant with IntelliJ

My daughters are doing a computer science class and using Replit for their java programming work.  It is not always working/available, so I set them up with IntelliJ so they can do their programming locally on their laptops.

Their teacher gave them a custom .java resource file called In.java and they use it for inputting data from the keyboard by calling methods from In.

I see lots of references to using .jars as resources, but not using .java files.  Where would I put the In.java file so they can call it in all their projects?

Thanks in advance

Bob