When you reach game level 15 you can start completing orders for the Yacht and get Experience points and Coins, as a reward.
First, you need to repair the Yacht's Pier. Once it is ready, a Ship will dock there, and you will have 16 hours to fill the crates.
For each filled crate, you receive Experience and Coins right after you pack it. In order to receive the main reward for loading all the crates, you absolutely have to click on the "Send ship" button, once all the crates are filled.
*If the Ship leaves on its own, even fully loaded, you won't receive this Reward!
The main reward for filling all the orders and manually sending the Ship includes Coins, Hospitality experience points, and, starting from game level 16 - a random Florin!
If you do not want to fulfill the orders, you can skip the Yacht, by clicking on the "Send ship" button. Once the Yacht leaves the dock (after pressing the "Send ship" button or when the time is over) the next one will arrive only in 8 hours, and you can see the required items in advance:
*To speed up the next Yacht arrival, bribe the captain with Diamonds!
Technically, you have 24 hours to craft the required items for the orders. And it is also possible to cooperate with your Neighbors, by asking for their help with the crates. You can help your Neighbors with their crates as well.
There are other vehicles in the game, that are related to the in-game quest lines: the Submarine is related to the Butterfly Palace construction process; A Ship with Rose Bouquets and Brad's Pink Yacht - both are a part of the quests on the Island of the First Accord.
Note, that you will have 10 hours to load the Submarine and 6 hours to load Pink Yacht. After receiving the related quests, a Submarine or a Yacht might not arrive right away, and there is always a chance that a usual Ship will appear instead. So there is nothing to worry about if you haven't collected all the quest items yet and then suddenly see a usual Ship instead of the Submarine. Simply fill the Ship or skip it, and there is a fat chance that the next vehicle that docks at your Pier will be the one you are waiting for!