Prerequisites :

JDK installed
AEM jar and license file available
Knowledge of “ls” and “java -jar” command

Steps:

Open terminal and navigate to folder where aem jar is kept:
Use command : java -jar AEM_6.5_Quickstart.jar -debug 30303
Assuming 30303 is the port number used for debugging.

On using above command, it should show “Listening for transport dt_socket at address: 30303”,
confirming AEM server is now ready for debugging at debug port used, 30303 in this case.

Connect AEM debug port to IntelliJ ? Check here.