Chili powder is the most practical way to always have a little fire at hand in the kitchen. It is made by grinding dried chilies, and the result varies a lot depending on the variety: there is sweet and fruity, smoky, and the kind that makes you cry.
In Korean cooking gochugaru, in flakes, is the heart of kimchi; in Indian cooking ground chili joins turmeric, cumin and coriander in masalas; in Italy a pinch is enough to liven up a vegetable soup, roast potatoes or a raw sauce.
Add it in small amounts and taste: it is easy to add more, impossible to take it out.