How to add a class on classpath in Intellij?

I have the following project structure in Intellij:

I am actually working with a maven project and all I wanna do is just run the project. Unfortunatelly I dont understand why but when I run the class called GenerateGraph it shows me the following error:

Error: Could not find or load main class graph.GenerateGraph
Caused by: java.lang.ClassNotFoundException: graph.GenerateGraph

I dont understand why this happens- it is the first time I encounter something like that. When I go on project structure I see the following:

Run configuration:

seems like it doesnt even see that the graph package has a class inside. Could someone maybe help me understand what has happened? Is it because I renamed the package after importing the project? Thank you very much in advance

Your project is not setup correctly.

You have reverseGraph marked as the sources root. In this case, src is the source folder.

The typical Maven project structure is src/main/java for non-test source files and src/test/java for tests.

What I'd recommend is modifying your folder structure:

1. Remove reverseGraph
2. Move src to the root of the project.
3. Add a src/main/java folder, and move your graph folder into that.
4. Reimport the Maven project in IntelliJ, and it should automatically flag the java folder in src/main as the sources root.

Most likely the dependencies are not correctly set up - because you do not have this project opened as Maven project in IDE. Please import this project as Maven project, see steps from Open an existing Maven project IntelliJ IDEA documentation section.