Vietnamese use annatto ( or achiote ) seeds in dishes mainly to add color to them. These tiny seeds have a mild flavor and add a red-orange color to the dishes. Saute or grind annatto seeds to bring out their aroma and color.
It is used primarily in Mexican and Caribbean cooking to impart a rich yellow/orange color. Annato seed makes a good substitute for saffron's golden coloring, at a fraction of the cost. It does NOT, however, duplicate saffrons unique flavor!
Another popular use for annato seeds is to make achiote oil. Cook the seeds in hot oil until their skin dissolves. When the oil turns bright yellow, discard the seeds and use the oil for cooking.
The seeds can also be ground with garlic and any variety of chili peppers for adobo paste.