BlueBrick is written in C# based on the .NET Framework 4.0 and needs Mono to be interpreted. So First you need to install Mono 4.0, which you can download following this link:
https://www.mono-project.com/download/

If you want some help on installing Mono on MaC OSX, please visit:
https://www.mono-project.com/docs/about-mono/supported-platforms/osx/

Once Mono is installed, click on the arrow on the right for the next step.