The use of gold earned

Hi @2005v and welcome here. You must be pretty new to the game if you don't know how to use your gold. May I ask what level you are playing at? It is best to keep some of your gold for the really difficult levels as it is the currency of Candy Crush and players who run out of gold find themselves forced to spend real money later on in the game.

You can buy boosters with gold. If you have none of a particular booster just click on the booster icon you want in game and you should get this sort of screen below. You can also click on your player icon at the top of the map screen to access your inventory, which will show all the boosters you have and allow you to buy more using gold.

If you fail a level you can pay gold for extra moves when this screen shows up. Don't waste gold on your first try unless it is to keep your win streak and you can clearly see you will pass with the 5 extra moves, because sometimes the game lets you win easily on your second attempt.

If you don't get these screens it means you are not connected to the internet. As far as I know you cannot use gold while playing off line.