Here is my experience with it.
First you need to find pieces of shipwreck maps.? You find them various ways, such as fishing, collecting, land battles as a reward, after trading, after completing quests.? Then use a piece, and check shipwrecks under the journal tab.? There it will tell you how many more pieces you need to complete the map.? After using the required amount of pieces, it will show you a map of where the shipwreck is, and how many stars.? The more stars the better the loot, but more damage your ship will take/higher level thieves in the ship.? Also it might tell you a required skill you will need, like archeology or something like that.
Once you know where it is, its better if you get into a fleet.? The more members you have, the easier it will be to narrow down the shipwreck.? Head toward where the map show where it is.? It will be in a specific sea, so you will have to sail around until you get to the right one.? If you have an aide, the aide will tell you if you are on a bordering sea, or in the right sea.? Once you are in the right sea, have your fleet split up.? Then use the salvage skill/or rope.? It will tell you what member of your fleet is closest to the shipwreck.? Have the other fleet members sail toward that person and split up around him.? Keep doing this until you narrow down where the shipwreck is.? The shipwreck is usually by a port.
Once you find it, the salvage skill will start raising the shipwreck.? Your boat will start taking damage.? The higher star the map, the more damage you will take.? Repair yourself, and have you fleet members repair you also(they should sail by you when you are raising it).? Eventually you will raise the ship.? Once it is at 100%, use the haul skill/or rope.? Start sailing toward the nearest port.? If for some reason the ship sinks again, use your salvage skill and repeat.
Once you are in port, you will see an option to enter shipwreck.? Make sure not to enter until all your members in your fleet are in port with you, as they will get extra goodies from the wreck.? When you are in the shipwreck, there will be treasure chests.? Some chests will be locked, so having someone who has the unlock skill would be a good idea.? Sometimes when you open a chests, thieves will appear.? The higher the star map, the higher then thief possible.? You will either get trade goods, while your members get a little extra, or an item.