There are many things to do on St. Charles Street like dining at the fabulous restaurants, check out the Visitors Center (or take a picture in front of the largest fleur-de-lis on the block), shop at the boutiques, and even take a ride on the streetcar. But nothing is more common than seeing the Uptown mansions and buildings. These are somewhat similar to the buildings of the French Quarter; however, they are copied after many European and antebellum styles. In the past, these were the extravagant homes of the wealthy Creoles of New Orleans, the upper crust of society.
You can see St. Charles in two ways, in my opinion. The first is to eat at either the Copeland's Cheesecake Bistro or Cannon's that have their own on-site parking so after a meal you can explore the street. The second way is to catch a ride on the streetcar from Canal, or at any stop along St. Charles Avenue. I don't think to ride the streetcar is too expensive; perhaps less than three dollars or so.