1. Under Taxonomy, click the caret to expand the menu.

2. To view additional levels of a category, click the caret on the left to expand the menu.
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3. When you've arrived at the deepest level of a category you'd like to select, click the checkbox on the right to add the category.
​Note: You can select as many more categories as necessary using the same process.
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4. When you're done using the picker, click the caret next to "select categories" to hide the picker and view your selections.

Depending on your brand, the channel you select in the category picker may determine the url of your content.  The first category you select will receive this "Primary" designation.