Option A. From a property, assign it to a category
From the list of properties, click a name to get its details. Scroll down and at the bottom you will see a box for 'Assigned categories'. Click the pencil icon and you'll get a form. Move the category(ies) from the left pane to the right pane and click 'Submit'.
Click the pencil icon either beside 'Assigned catgeories'...
...then move the selected category to the right using the arrow and submit.
Option B. From a category, assign properties
You can also assign properties to a category coming from the category itself.
Click the pencil icon beside Assigned Properties...
...then move the selected properties to the right using the arow and submit.