Setting Up Gradle and the JDK

I am new to java development, and to IntelliJ. I'm trying to open a project I cloned off of github (sagetv). When I did the cloning through IntelliJ, it noticed that sagetv is a gradle project, and offered to set it up that way for me. I chose to do so.

Unfortunately, I cannot actually open the project (i.e., get into the IntelliJ IDE) because the JDK is not configured properly. But when I try to go into Project Structure and configure the JDK, I get a dialog box asking me to pick a location for the JDK. It defaults to /usr/lib/jvm...but if you click Okay, you get an error message saying that's not a valid place to put whatever was going to be put there (then why default to that location? but that's another question).

How do I get this mess configured correctly?