Motor boat engines are the engines used to propel boats through the water. They are separated into inboard and outboard. Inboard motors are located inside the boat and the boat is steered with a separate rudder. Outboard motors are located outside the boat, usually mounted on the transom and steered by moving the entire engine using a handle. Inboard motors are generally more expensive than outboard motors and they require a box in the middle of the boat, taking up space, and they have been known to be a fire hazard. However, they are more fuel efficient, produce a smaller wake and in heavy seas they have a lower center of gravity adding to stability. They are also much quieter than outboard motors and generally have more power.
The outboard motor boat engine is very easy to understand pieces of kit. You attach it to the transom, set it going and you are off with virtually no control input. Being cheaper, they are more accessible and when you are done with the boat thing you can simply remove the engine and take it with you in the car. Also, if you decide you want more power, just buy a new one, no expensive modifications to your boat required.
Whichever motor boat engine you think is appropriate for you, carefully read the specifications and safety instructions to avoid awkward situations later on.