You can earn gems in the game by:

- Serving customers and getting tips

- Leveling up in the game

- Achieving your next chef rank in the achievements

You can earn gold coins from:

- Serving your clients the dishes you have made - you can see in the Academy how much each dish sells for once you have unlocked the Chef.

- Selling items on the Social Market to other players

- Selling items to the salesman Tex

- Completing an event in the Chill out area

- For free in the Local wholesale deliveries which you obtain every 6 hours

I hope this helps.