The way to add a store to your account depends on whether you possess a Head Office account:
If you possess a Head Office, you may create one in the "My Stores" tab; see here for info.
If you do not possess a Head Office, you must contact a Booxi representative to create the store for you.
*Note: by default, stores that have no associated Head Office are not "linked" to each other, which means that they cannot be displayed together in the booking widget, as shown below:
If you want them to be displayed together, contact your Booxi representative to manually link them.