Cooking for Passover is complicated and has provided an opportunity for Jewish culinary invention. Passover food has to be made with ingredients that don’t contain leavened ingredients. They also can't be made with forbidden ingredients like barley and wheat that can become leavened.
Since most Jews in the United States are descended from immigrants from Eastern Europe, they tend to follow the stricter rules of the rabbis in the Ashkenazi tradition, including extra prohibitions on legumes, such as peas, beans and lentils. If the family you are visiting is from the Middle East or North Africa and follows the Sephardic tradition, they might eliminate leavened food but still eat rice and legumes. Or the family might have been influenced by both traditions, and you might find them ridding the house of rice but still eating peanut butter on their matzah. There is a lot of variation.
The main restriction is on grains that might be ground into flour and fermented with yeast to rise. The exception is, of course, matzah. Matzah is a large flat bread made of wheat flour or other grains permitted on Passover. Matzah bakers mix the flour with water only and bake it immediately in a hot oven so that it does not have a chance to rise.
Jews have a long tradition of grinding matzah into a flour-like consistency, called matzah meal, to make ersatz versions of non-Passover foods. It can be very confusing to go into a supermarket and find Passover cereal, Passover pasta and Passover cake mix, when you know that traditional Jews are avoiding regular cold cereal, pasta and cake mix. This is just the modern version of Jews rising to the culinary challenge of Passover, to keep the laws that commemorate the Exodus from Egypt without giving up all of life’s goodies.
Your best bet for finding kosher-for-Passover recipes is a Passover cookbook or kosher cookbook, both of which are available at most bookstores and libraries.
Also, for a variety of traditional and innovative Passover recipes, see our Passover Recipes index.
The Guide to Passover for Interfaith Families is also available in PDF and Word formats.