Report and dashboard folder sharing
Key Takeaway
You share the folder, not the report or dashboard. Folder access level and user permissions work together. For example, a Viewer with the "Create and Customize Reports" permission can rename or delete reports in the folder but can't share the folder, because sharing comes with Manager access.
In Salesforce, you don't share a report or dashboard directly. You share the folder that holds it. Each user, group, or role gets an access level on the folder: Viewer, Editor, or Manager. What a user can actually do with a report or dashboard depends on that folder access level together with their user permissions, such as "Run Reports". To predict what a user can do, you check both.
Share the folder, not the report
To share a report or dashboard, you share the folder it's saved in, not the report or dashboard itself. When you save a new report or dashboard, it goes into your private folder by default. To share it, select a public or custom folder in the Save dialog box instead.
Private folders are for work you aren't ready to share. Reports and dashboards in a private folder are invisible to everyone except the person who created the folder.
When you create a new folder, only you and users with administrative permissions can access it until you share it. As the creator, you have Manager access to the folder.
Opening a report or dashboard takes two things: access to the folder it's saved in, and the right user permission. For example, to run a report you need access to its folder plus the Run Reports permission.