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 templates to help you quickly share a post for your business.
On the mobile app, you can create a new business profile (and switch between the businesses) by navigating to the "My posts" icon at the bottom of your screen then tapping the downward carrot next to your brand's name, which will bring up the "Select Business" screen. You can also tap on "Brand Settings" below your brand logo, scroll all the way to the bottom, and click on the blue "Switch or add business" button.
On the web app, you can do the same by clicking on the "My Posts" or "My brand" tabs then selecting the down carrot next to your logo.