It's pretty easy to get going!

• Download this -> https://www.jetbrains.com/idea/download/
• Start it up
• It will say "Welcome" and show a window letting you create a new project, etc.
• Click on "Import from source control"
• Pick "git"
• supply https://github.com/kotcity/kotcity.git for URL
• press clone (this will take a little while)
• It will ask to create a project. You would like to.
• On the next screen, say "Import Project from external model" and pick "Gradle". All the other defaults should be fine.

• Go to "View" -> "Tool Windows" -> "Gradle"
• Expand Tasks -> Applications
• Double click on run

The first time will take a little while because it has to download all the packages. After that it will be relatively quick.