You'll first be prompted to create a business profile when clicking through the welcome screen. Once you create a business profile, you'll see some related designs to help you quickly share a post for your business. 

You can create additional business profiles and switch between them by tapping the "My Business" tab in the lower right corner of the screen, selecting "Settings" next to your Business profile logo and selecting the name of your currently selected business in the upper side of the screen, which will bring up the list of your business profiles with the option to add more.