If you have more than one business location that you would like to manage with myPresences it is advisable that you add them under the one account (login). This makes it much easier for you to manage your locations and gives you a number of benefits. See Working with Multiple Businesses.
To add a second location (or any number of additional locations) simply click on your business name in the top header and in the drop down choose Add New Business.
This will take you to the new business page that you used to add your original location, see Adding your Business for more information on adding your new location.
Adding Peer Locations
If the business location you are adding is a peer of your existing business (or a competitor) and you already have a license then you can add up to 3 (depending on your license) peers or competitors so that you can track them against your own business.