To place the Teams or Players that have entered your tournament in to the bracket you need to seed them.
Before seeding ensure you've created your bracket and then you'll be able to seed the Teams / Players that entered your tournament onto the bracket. You also must reload the seeding page if it was opened prior to the tournament start time so that you get updated registration and checked-in player listings.
To seed your bracket click the Manage Button on your Tournament then Click Seed Brackets and Select the Bracket you've created.
Now Click Auto Seed and select Seed by Registration Order or Seed Randomly, then click Generate Bracket. Note: If you have a registration cap and more people are registered and checked-in than the cap allows, then you must seed by Registration Order first and then use the shuffle seeds button to randomize it before hitting Generate Bracket.
Once you've finished seeding you can Start your Bracket by Clicking Start Bracket Button and now your tournament will begin.
Here's a short YouTube video Tutorial on seeding your bracket after you've created it https://www.youtube.com/watch?v=PQedmE36lfA&t=52s