How to add and manage customer groups in PrestaShop 1.5-1.6
Each customer whether register or not is associated with one or more customer groups. You can use customer groups to set up various discounts, to select whether the customers from that group should see prices with or without tax, to limit the access to modules and to product categories.
In the admin panel of PrestaShop there's a separate section for adding, editing and deleting customer groups. To access it, go to Customers menu>Groups sub-menu.
Add Customer Groups
To add a new group, after you go to Customers menu>Groups sub-menu click on the Add new group button that's in the upper right corner of the page (in PrestaShop 1.5 the button is just Add new). This will open the form for adding new groups. Put a name for the group in the respective field. From the Discount option you can set a discount for the customers in that group. The discount will apply to all products in the store unless you also add a specific discount for particular categories. In this case the category discount overwrites the general one, but only for the specific category. From the drop-down menu Price display method you can select whether product prices should be shown with or without tax. This affects the prices shown in the catalog, the Summary and Payment steps of the checkout process and the cart block. From the Show prices option you can select whether product prices should be shown or hidden.
Keep in mind that a customer can be a member of more than one group, but each customer has only one default group. It can be set from the account options of the customer. When a customer belongs to more than one group, the settings of the default group are applied; they overwrite those of the other groups with which the customer is associated.
When you're ready with the options click on the Save button. The group will be created and a couple of other options will become available: one for category discounts and another for authorizing/unauthorizing modules. To configure them just edit the group.
Edit Customer Groups
To edit a customer group, go to Customers menu>Groups sub-menu and in the table with the groups click on the Edit button for the group. The edit form contains all the settings of the form for adding groups and two additional options. One is called Category discount and you can use it to add discounts only for particular categories. If you add a general discount from the Discount option and you also add a category discount for a specific category, then the general discount will not apply to that category (only the specific category discount). The category discount will be applied to all products in the category for which that category is the default one.
The other option that can be configured once the group is created is Authorized modules. You can use it to authorize/unauthorize modules. By default, all modules are authorized. If you unauthorize a module, the customers in that group will not be able to use the functions/settings provided by that module. Note that unlike other group options, with the Authorized modules option the default group is not the one that takes precedence. What's meant by this is that if a customer belongs to more than one group and a module is unauthorize from the settings of one of the groups, but authorized from the settings of the other, then the customer will be able to use the module. It doesn't matter which the default customer group is.
Delete Customer Groups and View Customer Group Information
To delete a customer group, go to Customers menu>Groups sub-menu, in the table with the groups click on the arrow that's next to the Edit button for the particular group and in the menu that appears click on Delete. In the same drop-down menu there's a button View. This will display a page with information about the group. It shows how the group's options are configured and a list of all customers in the group.
In PrestaShop 1.5 there's no such drop-down menu. The buttons for deleting and viewing are put directly in the table, next to the edit button.
Associate Customers with Customer Groups and Set Default Groups
From the account settings of each customer you can put the customer in any of the groups you have created, and you can select which is to be the default group for that customer. To do this, in the admin panel go to Customers menu>Customers sub-menu, in the table that lists the customers click on the Edit button for that customer, and on the page that opens use respectively the options Group access and Default customer group.
Limit Access to Categories
You can limit the access to each of your categories for each of the customer groups. You can do this from the settings of the category. In the admin panel go to Catalog menu>Categories sub-menu, click on the Edit button for the category and on the page that opens use the Group access option. If you limit the access for a group, then the customers in that group will not be able to open the page of the category and those of the products in the category. Keep in mind that a product can be put in more than one category. If a product is also in another category to which the group has access, then the customers from that group will be able to open the page of the product. Note also that if a customer belongs to another group (regardless of whether it's the default for the customer) that has access to the category, then the customer will be able to access that category.
For some more details and screenshots check out the tutorial on how to manage customer groups in PrestaShop 1.5 and PrestaShop 1.6.