To cite our sources you should refer to the particular item (for example a database or image), the project (or collection) it comes from, the VCDH, the University of Virginia, and the web address of the item.
For example, if you performed a search on Onancock: Its Beauties and Advantages the appropriate citation would be:
Onancock: Its Beauties and Advantages, The Countryside Transformed, Virginia Center for Digital History, University of Virginia (http://jefferson.village.virginia.edu/vcdh/jamestown/Musters/muster24.html).