Gold looks like a 3D "Sprite based" Cube, its color is gold, as its name says.
It used to reward users with 2 Gold each time they were playing a new game, by clicking a Gift Icon on the menu. You were able to collect 10 Gold a day by playing new games. Since now Free Gold by playing new games has been removed, you are now rewarded with 60 XP instead of Gold. (Gold reward from gift was removed on June 2018)
All ways to get Gold are listed on the Earn Gold page.