Can I buy multiple tickets in one transaction?

You can purchase multiple tickets from the Tickets/register tab, in a single transaction, if the event organizer has not limited it. Just use the drop down for each ticket type and select the number of tickets, and click on checkout.

In the checkout page, you can fill-out the details as requested by the organizer, check the boxes to accept the terms and conditions, and any other terms, and then click on place the order to go to the merchant page to complete the transaction.