Unable to set gopath

I have got go lang installed version 1.6.1/i386. Using UBUNTU 16.04.

Whenever am trying to download gomobile tool using

go get golang.org/x/mobile/cmd/gomobile it gives an error saying

caot download: gopath not set. Have tried looking for solutions online but nothing seems to work, maybe am doing it wrong. Someone HELP!

****AM NEW TO LINUX. Please try to be a little elaborate if possible and bare with me.