Apart from receiving new tickets directly from customers (e.g. by using the submit ticket form, the email piping functionality, or the Ninja Forms integration), you can also manually create tickets on behalf of your customers if required.
Within the tickets listing page (WP Admin -> Tickets) there is an “Add New” button. Clicking it will open a form that will allow any agent to add a new ticket by filling in all of the details manually. This ticket will then be treated as a regular ticket created using the built-in form.
You can also create a ticket from a comment posted on any of your posts or pages. To do so, locate the comment via the admin panel (WP Admin -> Comments) and hover over it. A “Convert to ticket” option will appear among the rest. Clicking it will redirect you to the add new ticket form with the fields prefilled using the details from the comment.