The easiest way of getting the software is to download the torrent file for the latest official SD card image from here:
Download Zynthian "Gorgona Omega" SD-image, configured for Kits v2 SHA1: 601ab5e58d3f08b7cda6f5821d396f6622e93106
Download Zynthian "Gorgona Omega" SD-image, configured for Kits v1 SHA1: 53ce2ba3c055698d27108750c2b80313f904c921
It's a 8GB compressed image file (plenty of soundfonts) compiled for Raspberry Pi 3. (Please, keep feeding the torrent after downloading!)
These SD card images include all the Zynthian software, properly configured for working with the official kits. Completely ready to use. Plug and play!
After downloading the SD-image, you have to write it to a SDcard. You need a SD card with a minimum size of 16GB, although you can use a bigger one if you want.
Finally, if you like, you can build your own SD image following these instructions: