If you purchase more than one ticket, you can assign those tickets before hand (for example, if you sell one to someone else) instead of having to deal with getting all the tickets yourself on event day and distributing them yourself. Who has time for that?!?
There are two ways to access the tickets you have already purchased. If you received an email confirmation of your event ticket purchase, you should see a "Transfer" link or button at the bottom of the email.
Simply click that, and you will be presented with a form that shows all your tickets. The blank lines are your unassigned tickets. This page will also combine all of your ticket purchases together if you used the same email to purchase them all. If you enter the new recipient's email address, they will receive a copy of their new ticket.
You can only transfer a ticket one time. If you need to transfer it again, to someone else, that will depend on the policies of your specific event and you can contact your event coordinator for help in making an additional transfer.