The Share tab allows you to share with Groups, Companies and Users. If the report is relevant to multiple users, you may find that Companies or Groups are the best way to make sure that the report is not only shared with all of the appropriate users, but also that any new users added to the Company and/or Group automatically get the shared report.
There is an important distinction between shared users on reports and shared users for scheduled reports which must be understood whenever sharing reports with sensitive data. Shared users accessing a link to the report, whether through the application interface or an email link, will run a query which presents the data based on the specific user's permissions, settings and access rights. A shared user accessing a report which was saved as static data (i.e. spreadsheet or PDF file) when the schedule was run will see the exact same results as the creator of the report because the report was run and saved under the settings of the report creator as static data for the other users to view. This important distinction is re-iterated in the explanation of the Report Output Format in the scheduled report settings.