How do I select multiple items in a single field?

Holding down the CTRL key (or Command key, for Macs) on your keyboard while you click will allow you to select multiple items in the same field. Once you let go of the CTRL key, all of the items you have chosen will remain selected. Make sure to hold the CTRL key again if you want to make more selections or remove selections; clicking an item without holding the CTRL key will remove your previous selections.