Q:

How to configure and structurize subproject using Intellij

Regarding the Joe Grandja presentation on OAuth2.0 in Spring Security 5.0 in the exact linked moment 5:01 

the project messaging-app is containing two "subprojects":
client-app and resource-server which are separate gradl/amven projects.
Here are the subprojects repo.
However, in IntelliJ - under Project window - both subprojects seems to be "joined"/structured somehow UNDER the messaging-app parent project which is like a container project for both of them. 
Questions:

How to achieve this kind of structure in IntelliJ for two (or more)
separate maven/gradle projects under third parent project? I assume that the subprojects' codebase is not under parent directory of parent proejct.
Are those child projects considered as IntelliJ modules?

A:

If the projects you want to see in the Project View do not have a common parent/aggregate project that can be imported in IntelliJ IDEA, do the following:

Create a new empty project (without any modules) via the wizard
Add the modules manually in the Project Structure | Modules dialog, click the + button, Import, point to the location of the build.gradle or pom.xml file you want to be in the project.

