When a user submits a ticket, a custom ticket status is applied to the ticket. The custom ticket status depends on which ticket status you have set as the default.
Ticket statuses allow for tickets to be tracked through the various stages of it's life cycle. For example you may set up a default status as 'New' which is applied when the ticket is submitted. When you have replied to the ticket, you might set the ticket status to 'In Progress'. When you have solved the user's issue you might set the ticket status to 'Solved'. Once a support ticket has been dealt with you might set the ticket status to 'Closed' or 'Archived'.
You can set up as many statuses as you want, with any meaning ascribed to them, and you can move tickets between statuses freely. This allows you to manage support tickets and organise them with ease.
In addition to using ticket statuses to manage tickets, you can choose emails that will be sent when a ticket moves into that status.