When you log in, you will arrive at the dashboard. You will see relevant information about projects and tasks, depending on your user role. Admins have access to all features, and will see an overview of all items in the system. Users with other roles will only see projects and tasks they are involved with, with limited view and edit capabilities.
The first time you login, the dashboard will look a bit empty. Don't worry, this will change soon!
You will probably notice that the time at the top of the page is incorrect. This is because by default the system uses the UTC timezone and you probably live in a different timezone. You can change this by clicking on the time. This will take you to the localization tab of your profile.