Full-time agents are those in your core support team who will log into your helpdesk every day. Please navigate to Admin -> Team -> Agents -> Click on new agent to add this person to your portal. In the case of occasional, please switch the radio button to this option, 

Occasional agents are those who will only need to log in a few times every month, such as the CEO or your field staff. That way, people from other departments in your business (like sales and marketing) can log in and take care of specific customer queries from time to time, without you having to purchase an additional agent seat for a whole month.

You can add an unlimited number of occasional agents to your helpdesk no matter how many full-time agents you have paid for when you picked a plan. 

Each occasional agent will use up a Day Pass for every day that they log into your support portal. For example, if you have one day pass and an agent logs into the helpdesk at 8 in the morning, the day pass will be valid until the end of the day (00.00 hrs).