They can be used to fill in around stepping-stones and under other plants. They make a great way to prevent weeds from taking hold and they add depth and a finished look to a garden by covering bare dirt. There are groundcovers for almost every kind of garden culture from damp shade to drought tolerant.
Whatever plant is used, they all need special care while getting established. They should be kept well watered until their roots take hold and integrate well into the native soil. Be sure to note the growing conditions where the groundcover is going to be planted and either consult a good reference book or visit a nursery that can help choose the plant that will grow successfully in your space.