If you have several users in your account, you might want to make tickets created by any of them visible to the entire team or limit their visibility.
You can change this easily from the Users page.
Select Settings ->Users in the main menu.
In the top right, you will see a box where you can switch between the options. By default, all users can view their own tickets only. Toggle the switch to the right to let each user view tickets created within your team.