By default, only you can see the reports you create. If you want them to be viewable by other members of your organization, go to Settings > Sharing and select the members with whom you wish to share it and the access you want them to have. Those with Read Only access will be able to view but not alter the report. Members with Edit access can change any aspect of the report, change its sharing settings, and delete the report. If you want to grant access to everyone in your organization, select Everyone.
Changes will not take effect until you hit the Save button at the bottom of the page. At that time, you may choose whether you want to notify users gaining access to the report.
Please note that you will not see the Settings or Sharing options if you do not have edit permissions for a report.