Seamanship is loosely defined as the art and practice of operating a sailboat. It involves much more than the mechanics of making a boat go through the water from point A to point B.
Things that are different with the mechanics of operating a boat is that 1) it steers from the rear and 2) there is no control with the rudder until water is flowing past the rudder. While this seems like a simple and obvious concept, understanding how this translates into operating the boat. Another important thing is that there are no brakes on a sailboat other than using the wind or the motor.
Basically, the guiding principle is that sailing is 95% preparation and 5% execution. One has to plan for what happens when things fail. An example here is if you are approaching an area that is shallow with rocks on one side and the tidal current is pushing your boat towards those rocks. If one is motoring, the skipper has to take a course that will allow enough time to get the sails up (if there is wind) or put out the anchor if necessary tot keep from being driven into the rocks. That means practicing getting the sails up within 20 seconds or so or getting the anchor out quickly. If sailing is an option then there will probably be no problem unless the wind dies. Even if the water is too deep for the anchor, putting it out might help as the water gets shallower and the anchor takes hold. In any event, one should be ready to make an emergency call to the coast guard on VHF channel 16 to the coast guard or any nearby boat. Channel 16 is the universal hailing channel that all boats should be tuned to while on the water. It is required if you are nearby to render assistance if at all possible. The law protects the good samaritan.
These may seem obvious, but unless one has thought about this in advance and actually practiced things like putting up the sails quickly, one can panic in stressful situations.
Seamanship also involved knowing the navigation rules and rules of the “road”. The number one rule is that even if you have the right of way, you are required to avoid collision. Knowing when you have the right of way (also known as the stand on vessel) or when you have to give way is an important aspect of these rules.
Other aspects are knowing where everything is on the boat and being able to quickly isolate problems.