Do you remember playing with straws and trying to put them together to make a long chain? Well, imagine that on a much larger scale - like really, really big straws.
A pipe-laying ship is a huge boat that has a long, narrow deck called a "pipe-lay stinger" which is used to lay pipes on the ocean floor. Think of the stinger like a really long straw that the ship puts in the water.
The ship pulls pipe sections from on board and feeds them into the stinger, which then lays the pipes on the seabed. These pipes are used for things like transporting oil or gas from offshore drilling rigs to onshore facilities, or for carrying fresh water, sewage and other things that need to travel across the ocean floor.
The ship also has big cranes to lift and move the heavy pipes around. Once the pipes are laid, they are often connected together using machines on the ship to make sure the pipes are secure and won't leak.
So basically, a pipe-laying ship is a really big boat with a long deck that lays pipes in the ocean to help transport things like oil, gas, water, and sewage.