Aft: This is the back of the boat, or at least towards the rear end, where the propellers will be. If you are to meet someone or see something towards the aft of the ship, head to the back.
Berth: These are the beds which are built in to the cabins you sleep in. A cabin is usually described as being either single or twin berth, which simply means whether they have one or two beds. A twin berth cabin will have two beds, and will usually be larger than a single berth.
Bow: This is the front of the boat, and is a good place to get grand views of the ocean, or of the country you are approaching.
Disembark: This means to leave the ship. When you arrive at a port, the passengers will usually disembark, or get off the ship to have an explore around. During this time the ship's staff will usually tidy the cabins and clean the ship ready for you to return. When you return to the ship and get back on, this is called embarking.
Leeward: This is a good place to be - it means that you are on the side of the ship which is away from the wind. The side which catches the wind is called the windward side, and the side which is sheltered is the leeward. Of course, as the wind changes and the ship turns, these sides may well change, but making sure you have booked your seat on the leeward side will ensure you have a sheltered place to enjoy the view.
Life Preserver: These can often be life jackets, which we're more familiar with, but are not necessarily always jackets. They may also be vests, or even rings. Basically, a life preserver is any device which floats and is designed to help keep a person afloat in the water. There are always at least as many of these as there are passengers, so every passenger will have access to one of these.
Muster: This word means to come together as a group. It may sometimes be the case that for safety drills, or for other events, you are called to muster. This simply means that a group will meet together.
So if you are asked to muster on the leeward side towards the aft, you know you have to meet with your group on the sheltered side of the ship towards the back! You see, it's not that difficult!
In truth, you'll probably find that most modern cruise liners will not use this kind of terminology, and those people who do use these words are old traditionalists that like to show off their naval knowledge! However, there are times when these words might be used, and having some idea of what they mean may help to save you a little time and less fluster trying to work out where you need to go.