Okay, i have played this game since 2004, yet i have never used officers because they always died and never helped me with anything... can someone explain how they work and if i can use boatwsain only to fight in sea battle/land fighting, and if i can use navigator/canoneer/quartermaster as only for my ship.
First, are you playing the stock, unmodified game, or are you playing one of our mods? If the latter, which one?
Both in the stock game and in mods, you can control which officers join you in boardings and on land through the "Passengers" screen via F2, as
@Talisman said. In the stock game, only those selected to join you will use their skills, but I always found that they died in boarding actions even if they had high "Melee" skill and good equipment, so I always deactivated them using "Passengers" shortly before boarding. They generally did better in land battles and if I was facing a band of four thugs, the officers could at least keep some of them busy long enough for me to kill the thugs before they killed my officers.
In Build 14, you can use the "Passengers" screen both to assign officers to join you and to assign them different jobs, though they'll normally have only the skills associated with their original jobs when you hire them. Also, when on land, you can talk to the officers who are with you, go to "About you", and tell them to sit out the next boarding. They'll still join you on land, though they won't follow you into dungeons, but they won't join you in ship boardings. "Melee" skill is now more useful and an officer with high "Melee" is much more likely to survive battle both during boarding and on land, especially if you give him a decent sword and either battle armour or gold armour. Meanwhile, all officers, including the ones not assigned to join you, will contribute skills according to their jobs and you can see the cumulative effect of all your officers' skills plus your own by going to the "Passengers" screen and clicking on yourself.