A daily fantasy sports contest ticket can be used for free entry into a contest, but you must redeem it before it expires. You can receive entry tickets by winning them in specific DraftKings contests.
You can check if there are any tickets available to you from your Account tab if you are using the mobile application or from the My Tickets page if you are using your browser.
To redeem a ticket, look for the 
icon in the lobby to find a contest in the lobby that matches the description on the ticket. Once you have drafted a lineup and are ready to submit your entry, the submission button should display Enter Ticket instead of a dollar amount.