The 'Design Management' page is where the section is that allows you to adjust the price of the shirt and choose which items are available for sale in your store.
This is a screen shot of the 'Design Management' page (the arrow is pointing at the place you can adjust pricing)...markup):
To get to that page do the following while logged into you store dashboard:
Then click 'My Products':
Then click the add (+) symbol:
It will take you to the Designer studio. There you can choose a style...which is what will be shown by default in your store:
After the design is placed on the shirt and the shirt color and style selected...click the 'Add To Store' button. You will be directed to the 'Design Management' page:
In the design management page you can decide if you want all styles and colors to be available for your design...or click as shown below to update to only the colors and styles you want sold for your design: