The cardinals seem to enjoy sunflower seeds. Birds also need water. They drink it and bathe in it. Remember to put their food and water source in a place where there is protection from their predators. Shelter is important.
Birds use shelter for protection from the elements.
Trees, shrubs and native plants provide good protection. Birdhouses are mainly used for nesting purposes. If you wish to build functional birdhouses, find out the requirements for the species you want to attract. Functional birdhouses should be able to be cleaned yearly. There is a great difference in a functional and a decorative birdhouse.