How do I associate tickets with a category?

The relationship between category and ticket is more like a set and subset.  You can have more than one category on the platform and each category can accommodate one or more than one tickets.    

So, if you want to have category based tickets then first create all the tickets. After this click the   "Add Categories" option on the ticket/Registration page. A page pops-up which has option to add Categories.  Click the "Add New Category" button and give a suitable name and then select one or more than one tickets from the list to be associated with the category.  Click save and category to ticket association is completed. This way, you can add more categories and attach tickets to it.