Step 1: Open a terminal application (Try shortcut CTRL + ALT + T or look in the application menu for “terminal” )

Step 2: Type or Copy past: sudo apt-get install curl  

Step 3: Type or Copy past: 

bash <(curl -s https://raw.githubusercontent.com/varnamproject/govarnam/master/quick-installer.sh) 

Follow the instructions shown in terminal to complete installation.
Step 4: Add Varanam language in  keyboard settings