The very first thing you'll see when you click the "buy tickets" button is a list of available ticket types for the specific event you are trying to purchase tickets for.
Some events will only have one ticket type, while others may have many.
If an event offers upgrades/add-ons, they will be selectable after selecting tickets. Some upgrades/add-ons are only accompany certain ticket types. Please read the event description or visit the venue website to learn more before purchasing.