The reputation shows how helpful a user is in the community based on their activities in posting, liking, etc. The the virtual currency on the other hand, is used to reward users for participation in a certain Q&A.
Every time a member finds your content useful and likes it, when you post a content, any other types of activities, you will earn points. Community admins can install the reputation app and can customize the rules for the reputation points. Learn more here120.