As the name suggests, a Committee of the Whole House is when the Committee Stage of a Bill is taken on the floor of the Commons. Such committees normally only take place for emergency Bills, for certain clauses of the Finance Bill and for the clauses of Bills that have constitutional significance. All MPs may table and move amendments and vote and procedure is the same as in a Standing Committee.
Normally, the programme motion passed after Second Reading will timetable proceedings in a Committee of the Whole House. Private members' Bills are never considered in Committees of the Whole House.
When the Committee of the Whole House has concluded its deliberations, it reports the Bill, with or without amendments, back to the House.