A convenient feature in Freebase is called 'autocomplete'. You may have noticed as you were keying into many of the fields in Freebase that it was trying to match your result for you. You can expect a field to autocomplete for you whenever you see a little link icon to the left of the input box.

When the text you input exactly matches something in Freebase, it will be selected for you (highlighting it in blue) in which case you can simply click 'return' to commit it. If you have a close match, you'll likely see a number of options based on what Freebase thinks you're looking for. Additional information may be displayed to help you differentiate the options in the list. If you think you see the option you're looking for, you can select it with your mouse or by using the up or down arrow keys on your keyboard. 

If no match exists, you may also be able to create a new item by clicking the 'create new...' button at the bottom of the list. You can also use 'shift-return' as a shortcut to accomplish the same thing.