Both of these are leaveners, but they react under different conditions. Both need to be stored in a cool dry place. Once you have opened the container, be sure to keep in a sealed bag or container. Also note that baking powder will lose its effectiveness around the one year mark.
A bit more information: Baking soda reacts with an acid to release carbon dioxide which gets caught in the dough or batter and causes it to rise. It requires the presence of an acid ingredient, such as chocolate, vinegar, a culture dairy product, fruit juice, or molasses.