tar -xzvf IndigoRenderer_x64_v3.4.18.tar.gz
This will extract the archive into the directory dist/IndigoRenderer_x64_v3.4.18
cd IndigoRenderer_x64_v3.4.18/ ./indigo_console -v
Which should print out something like
Indigo Renderer v3.4.18, Linux 64-bit build.
To run the graphical user interface, run ./indigo.
You are now ready to run Indigo.