The breadboard has nothing to do with making a sandwich but is a convenient and simple way to make electronic circuits without having the need to do any soldering. You would use this while prototyping, practicing, playing around to see if it works.
There are various sizes. There is a full size of 830 points, half size 400 points and mini 170 points. The points refer to the number of holes where you put your wires and components in.
The first two boards have a positive and negative rail running down each side. The mini does not. The positive and negative rails run lengthways down each side of the board. The other rail run across upto half way on each side of the centre.