If you do not know how to access your registration site editor, you can find instructions here.
Once you have opened your registration site editor, navigate to the "Tickets" tab. To create your first ticket select the "Add Ticket" button. A menu will appear asking for ticket name, description, type/price (paid or free) and ticket quantity. You will also have the option to hide the ticket from registrants. If you are creating a paid ticket, you will have to setup your Stripe account before doing so.
Once your ticket has been created, it will appear under the "Manage Tickets" tab. If you have multiple tickets you can change the order they appear with the "Reorder Tickets" button.