Harissa is the North-African version of a hot chili sauce. It is made of red chili peppers, tomatoes, cumin, coriander and garlic. It is used in tagines, sauces and soups. Nowadays you can get it in tubes and pots in the supermarket.
Moroccan use it at the table. You take a spoonful of your sauce, at a bit of harissa on the spoon, stir it a bit and then pour it in your bowl or on your plate.