Here's the breakdown:
* Original Series: The original series, written by Mildred Wirt Benson, is considered the "canon" of the Nancy Drew books. They are numbered from 1-56, and the order you should read them in is simply by number.
* Carolyn Keene: The "Carolyn Keene" name was used to represent multiple authors who wrote Nancy Drew books after Mildred Wirt Benson. The order of these books is also numbered, but be aware that some of these stories might not have the same tone or quality as the originals.
* Other Series: There are also spin-off series and different re-imaginings of the Nancy Drew characters, but these might not be in the same continuity.
To find the complete list of Nancy Drew books in publication order, a quick search online should give you the information you need. You can also look at the back of any Nancy Drew book, as they often include a listing of the entire series.
Let me know if you have any other questions!