We assume that you have already logged into Zen Cart.
Click on the Customers link found on the main menu as shown below.

Then click on Customers link, like the one below.

As you can see, there is no customer record in this store. You are actually not able to create a new customer here. Basically, customers create their own accounts on your site.
You can click to edit an account anytime, with the customer highlighted. Then you can either edit, delete or email your customer accounts by choosing the respective buttons found on the far right of the screen, like the one shown below.

That’s it, you now know how to manage your customers in Zen Cart.