The word sole has two main meanings:

1. The only one; single and exclusive. When you have sole responsibility for feeding the class hamster, you're the only person in charge. A sole survivor is the only person who lived through a disaster. The sole purpose of a lighthouse is to warn ships away from dangerous rocks. When something is sole, there are no others like it in that situation.
2. The bottom of your foot or shoe. The sole of your shoe is the part that touches the ground when you walk. After hiking all day, the soles of your feet might feel sore. Shoe soles can be made from rubber, leather, or other materials. Animals like bears and dogs also have soles, though we usually call them paw pads.

The word sounds exactly like soul, which means the spiritual part of a person, but they're spelled differently and mean completely different things. When you're writing, remember: sole for “only one” or “bottom of a shoe,” soul for the inner spirit that makes you who you are.