The Mortar lets you grind and mix items entirely by hand. It is perfect for early game crafting or when you just want to do things the old-fashioned way.
Usage
Right-click items onto the Mortar to add them as ingredients. Fluids can be poured in or drawn out with a bucket, or with any other item that carries fluids.
To grind the items, hold right-click on the Mortar with a Pestle. If you want to mix things instead, hold right-click with a Ladle. Each tool wears down a little bit with every use.
When you are done, you can shift-right-click with a Pestle or Ladle to rest it decoratively on the Mortar.
Recipes
On its own, the Mortar comes with a set of built-in recipes. Grinding generally pays better by hand than in the crafting grid: a bone gives four bone meal instead of three, a blaze rod gives three blaze powder instead of two, and flowers and other dye sources give two dye instead of one. It will also work cobblestone down to gravel and gravel down to sand. Mixing turns dirt into mud, clay balls into a clay block, and sand and gravel into concrete powder.
With Create installed those built-ins step aside, and the Mortar instead runs Create's Milling recipes when grinding and its unheated Mixing recipes when stirring. Crushing Wheel recipes are also supported but are switched off by default, since they overlap heavily with milling. All of this can be toggled under Create Compatibility in the config.
Glass bottles only work as fluid containers when Create is installed, as Create is what teaches the game how to fill and empty them.