Managing a catalog in multistore mode
In the multistore mode, some of the PrestaShop administration pages feature a prominent drop-down menu, titled "Multistore configuration for". This menu gives you the context of what you are doing: it enables you to set the shop or shop group to which the changes you are making are applied.
Likewise, if you change a product while in the "All shops" context or in the context of a shop group, some fields will be disabled: since they have a global impact, you cannot edit them. If you really need to edit this content, each field has a box that you can check to edit that field in all the shops under this context.
If you edit a disabled field, the product is created in all the shops of the context which do not already have it in their own catalog. Make sure to double check your context.
By associating the new stores with a given category, any change in this category will impact all the stores which are associated with it, even if the stores are from different store groups. You can, therefore, change the category's content once and for all from one place, including its products.
If you want to have different customer groups for each store, you must create a new group and use the "Multistore configuration for" selector to associate the group with the current store or store group.
If the option "Share customers" has been disabled, then your customer list will need to be empty before you can enable this.
If you'd rather keep your customer list you can do the following:
Sharing customers between the shop group has have now been enabled without the loss of customer information.
It is possible for stores within the same store group to share orders: all you have to do it set the proper option when creating the store group.
If the option "Share orders" has been disabled, then your order list will need to be empty before you can enable this.
If you'd rather keep your orders you can do the following:
Sharing orders between the shop group has have now been enabled without the loss of order information.