How in the world do I get the debugger to work properly?

How does someone who is completely new to RubyMine set up the debugger to work with a simple .rb file with a main method, essentially "hello world". I am trying to learn Ruby and I've spun around for about 4 hours now on how to properly configure my "gems". Is there a step by step guide anywhere that starts from bare bones and could walk me through the configuration of the debugger?