There are multiple different types of items on the Kitchen board. Here's an overview:

Generators: These are the source of all items in the game. You start by making a grocery bag and a drinks tray, but there are many more to unlock and upgrade. Tap on a generator to create items.

Items: The food, drink and other goodies that you create in the game. Basic versions come from generators, but you will need to merge them to create better food and drink that customers want.

Covered Tiles: Early in the game, a lot of space on the board will be covered up. To uncover these tiles, you need to make a merge NEXT TO the covered tile.

Locked Tiles: You can see items on these tiles, but you can't move them — they're stuck in place! To unlock these tiles you need to merge the stuck item with another identical item.

Bubbles: Sometimes a generator will create a bubble. Inside is an item, but you need to spend gems to unlock it. If you don't, the bubble will instead become a coin.