Described as 'Indispensible For All Crew' this excellent little pocket sized volume, companion to the long established Reeds Skipper's Handbook and clearly written by an experienced practical sailor, the claim is amply justified. The book dispenses a wealth of guidance on how to go about being an efficient and valued crew member on a sailing boat. It is specific to sailing; there's not much here to do with motor cruising except in subject areas common to both.
The book is particularly suited to those new to sailing and deals comprehensively with living on board, deck seamanship, knots and line handling, steering and the points of sailing, basic navigational routines, safety at sea and much else within its 158 full colour and liberally illustrated pages.
If you are contemplating your first sea passage on a friend's, or relation's boat, then get a copy and read, learn and inwardly digest as they used to say. If you are that friend or relation give your prospective novice shipmate a copy to read before you set sail.