Tickets for your event are sold in Packages that can have one or more tickets. Each package can be free assigned a cost, and a benefit amount. Once the quantity of packages you've allotted are sold, the package is marked sold out. Packages can be hidden or set to expire (e.g. early bird package).
To manage your packages, from your event's Impact homepage open the packages menu from the Events menu on the left.
From the menu, you can add or update a package. The Package Edit screen looks like this:
Note: All field with an asterisk (*) are mandatory