Depends on what you mean by "a single normal user can flag a submission". Any user with sufficient karma (30-odd?) can click "flag". The number of flags a submission has will affect its ranking, and with a sufficient number of flags, the [flagged] tag will appear.
Note that other actions (including voting on the submission, and commenting/participating in the discussion) also affect ranking (according to the FAQ).
Note that other actions (including voting on the submission, and commenting/participating in the discussion) also affect ranking (according to the FAQ).