If you have the Time & Expense subscription package, you get access to a limited number of reports. Check out this article for details: Core reports by subscription packages. However, the default Time & Expense security profile does not give you access to the Reports screen. You can only see some of these reports from the Time Entries (or Expense Entries) screen by clicking More > View Reports. If you want to see all these reports in the Reports screen, you should ask your Core administrator to customize your security permissions and give you access to the Reports screen. Check the Core Help for more details on customizing security permissions.