On the dashboard, the two most important windows in TPP are the Summary Screens. They look like this:
On the left is your business summary. You can have up to 8 businesses in the business summary. To add more businesses, click "Companies" on the left nav:
On the right, is your personal summary. This is a representation of your personal tax projection and will show you how much tax you may owe.
If you want to edit these summaries, or see the details of the summaries, you can click the edit button on each of them.