The unit ORB (Operational Record Book) was something kept by every unit, MUs, Squadrons, OTUs etc, and also at Group and Command Level. At Squadron level it was generally down to the Adjutant to write the entries, with the actual typed entries usually made my the admin staff (Orderly Room Sergeant, WAAFs, etc). The amount of detail varies depending on who was compiling them, some are very useful and full of detail, others rather sparse.
The form they took were individual pages typed up, and then inserted in a cover when the page was full. Most Squadrons would compile a brief day by day summary, with a fuller operational summary for each operation, including the crews participating, time up/down etc, after that.