It is the root tubers of the plant that are called ground almonds, chufa in Spanish. The raw tuber has a slightly chewy consistency and tastes like something between coconut and almond. After harvesting, ground almonds are washed and dried to be able to be stored for longer periods.
Ground almonds can be used raw or cooked. The raw, dried tubers can be eaten as is (preferably soaked for a softer texture) or ground into flour that can be used in baking. It can be used in the same way as almonds. You can also squeeze the oil out of ground almonds.
However, the traditional thing is to make a so-called Horchata de Chufa, a nutritious and healthy drink. Horchata de Chufa is ground almonds mixed with water to make a "ground almond milk" and is a common drink in the Valencia area.