Tea Leaves are an item added by the food plus mod as a crafting ingredient.
It cannot be eaten on its own.
These items are found randomly while breaking grass, much like generic Minecraft seeds.
Unfortunately, there is currently no renewable way to obtain tea leaves through farming, as there isn't a way to replant and grow your own tea leaves.
A plant, known as a "Tea Leaves Bush" does exist in the latest version of the mod, but it cannot be planted with either Tea Leaves, Dried Tea Leaves, or even a Tea Bag. So you'll just have to wait on growing your own personal tea garden.