You will need to install erlang, and rebar3. I recommend following the instructions from JetBrains: Getting Started with Erlang.

When you open this project with IntelliJ I recommend that you do

File | New | Project from existing sources 

Then be sure to select "Erlang" as the project type, and configure the rebar3 location correctly, (There is a copy of it in this repo).

If you're having trouble executing the 'main' application, check your module path in your Project Settings. I found I had to manually set the module compile output path to '_build/default/lib/gilded_rose/ebin'. The test output path seemed to be correct as '.eunit'

$ rebar3 compile

$ rebar3 eunit

To run for 30 days, I think this ought to work but I tend to run it through the IDE instead:

$ erl -pa _build/default/lib/gilded_rose/ebin -pa . -eval main:main([30]). -s init stop -noshell