Statistics

Admins open Administration → Statistics for instance-wide usage, refreshed every 30 minutes (GENERATE_STATS_CRON):

• Users, Files, Storage (with the part in the trash) and Views totals
• Views: file views over the last 12 months
• Top uploaders and Storage per user
• File types: the most uploaded types
• Near their quota: users who have used more than 80% of their usable space

Each user's own usage is on Settings → Storage: used space, Usage by type, Largest files and Duplicates.

For what happened rather than how much, see Logs.