The easiest way of getting the software is downloading the last official SD image from here:
This SD-image include all the zynthian software properly configured and ready to use. Plug and play! ;-)
After downloading the SD-image, you have to write it to a SD-card. Depending on your OS you have to choose how to create the SD-card. You need a minimum size of 16GB for the full Gorgona image and 8GB for the Gorgonilla lite image. There is a really good manual for this at this link.
If you prefer, you can build your own SD image following these instructions: