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 "Brand settings" button. At the very top of the page, if you tap on your business name with the downward carrot next to it, it will bring up the "Select Business" screen. You can also scroll all the way to the bottom and click on the blue "Switch or add business" button. Here is a video: How to Create or Switch Businesses on Mobile
On the web app, you can do the same by clicking on the "My brand" tab then selecting the down carrot next to your logo.