What airline are you looking to book? You will get a lot more helpful information here if you provide that. There are quirks to most carriers, but the bottom line is that you are usually checking a box which limits the search to awards, redemptions, points, miles or some other term, and which then displays what is available for the date, route, and class of service you have selected. Some carriers may offer redemptions with a cash component.
If you provide more information, you will get more useful information.