To use PayTabs payment gateway for selling Tickera tickets, you will first need to create a merchant account here.
Once you have finished creating your merchant account you can immediately head to Tickera to set it up as only your PayTabs username and password will be needed to set it up for use with Tickera.
So you just have to navigate to Tickera>Settings>Payment Gateways, check PayTabs icon and input your account information: