If you want to sell items/buildings on the farm, follow these steps:  

1. Tap and hold the item you want to sell until the yellow arrow lights up.  

2. Select the gold coin wallet icon.

If you want to sell items in the Storage, follow these steps:  

1. Tap the item you want to sell.  

2. Select the quantity you wish to sell.  

3. Tap the sell button.

Please note: Not all items or buildings in the Storage can be sold. Some unique and important items in the game cannot be sold!