You will only need to enter your items to your webshop once. You can then decide which items you want visible in each webshop, and all administrative control is handled from a single location. It is not necessary for all of your webshops to be on the same domain either. Each OpenCart multistore can have its own domain and appear to be its own webshop with separate theme, banners, and modules. Because of this your customers do not need to see that several online shops are running from the same backend. You choose what items are visible on each webshop and what amount is being charged, this can be different for each webshop.