The shipyard is exactly what it sounds like it would be, a place to buy ships! This is important as a new player because without a ship you cannot go to different ports. As you progress upgrading your ship is just as important since a higher leveled ship will give you a much better chance of winning when you are attacked by other players.
You can purchase a ship with either gold or spice.
When upgrading your ship it’s important to check the stats of the ship and make sure you’re set up properly. If you’re built for speed you want to make sure you’re not downgrading your speed when upgrading your ship.
An important part of the game that I myself did not know about right off the bat was ship modifications. Modifying your ship gives it further upgrades and can help you in naval attacks and when attacking in game characters. There are several items obtained by quests/comps/trading with other pirates that you can use to change the stats of your ship.
These modifications get listed in a table to show you the stat boosts they provide. Finding the best items can give you quite a boost when attacking other players and usually become the deciding factor in winning or losing.