If you cannot see Records on a Report, the first course of action is to clear the Filters to see all available data that the Report can show.
Note: The platform remembers the last filter applied.
To clear an existing filter simply click the 'x' next to the filter funnel in the top right of a List Report.
If this is not successful then the next step is to check if there is a Base Filter. If one is present then it will be indicated next to the 'clear-able' Filter funnel as seen below - for the removal of this however, you will need to contact your system administrator.
If there are no Filters on the Report this means it is likely a Record access issue. Users can only see Records if they belong to a Team that has got access rights to them.
See here for more on Record Security and access.
See here for more on establishing Teams on your site.