Gritty things have a rough texture that makes them feel like they're coated with sand. After a day at the beach, you might come home with gritty arms and legs.
A baking project involving corn meal might result in a gritty counter and a gritty kitchen floor, and one shake of your dirty dog will leave you with a gritty couch. Grit is a tiny particle of sand or stone, and gritty means "covered in grit." A second meaning of gritty is "showing bravery and spirit." When you stick with something no matter how scary or difficult it is, that's gritty.