The Lens Grinder is a machine that uses Energy to create Lenses. For example you can create Crystal Lenses by placing a block of the corresponding crystal into the Lens Grinder and selecting the Lens recipe associated with that lens.
The Interface and Grinding Lenses
By default the interface displays Categories of Lenses and you'll need to select a category before selecting a program. If you need to go back to the Cateogory selection screen you can press the arrow button in the top left of the GUI.
Before you start grinding lenses you will need to supply it with some energy.
To grind a lens all you need to do is place a regular Lens or a Crystal of the corresponding Crystal Lens that you want to craft and then select the crystal lens type you want to craft.