When you hold down left click on a tile, it'll show you all of the recipes for that tile.
When you hold down left click on an item, it will flag the top right of some tiles. The flag indicates that the item is used in a recipe on that tile. It'll be light blue if you've discovered all the items needed for the recipe and dark blue if you still need some. If you hold down right click instead, the game uses the result of the recipe instead.