Indexing Your Files
Assets won’t actually show any files until you’ve indexed your upload directories. The initial indexing might take some time, depending on how many files you have. However future indexes should go much quicker, since Assets will only have to index what’s changed.
To Index Files
Add-Ons → Modules → Update Indexes
You can also re-index an individual folder by clicking the “Refresh” button at the top-right of Assets’ file manager, or from its fieldtype’s file selection modal.