A ticket is simply a form you will use to gather the information needed to support your users. There will be a default ticket available when you first set up your system however you will most likely want to create your own Ticket Types for your business that suit your needs.
Any inbound request, whether it was created by a customer, a member of your staff, or a member of the public - via a ticket form or by sending in an email - creates a ticket in your Inbox.
Tickets can be anything from internal requests to customer support requests therefore your Ticket Types are flexibly customisable allowing you to create a Ticket form that can capture all of the information you require.
An example Ticket below shows a support ticket for an IT Support Request from an internal department and you can see it asks for a description of what piece of equipment they are requesting support with.
Head over to Managing Ticket Types for more details on how to create your own Ticket Types.