Theory:

Imagine cutting open a match box across all of its edges, and laying the figure thus formed flat. The outline thus formed is called its net.
Net of a \(3-D\) shape
The outline formed when a \(3-D\) shape is cut open along its edges is called the net of a \(3-D\) shape.
 
In other words, the net of an object is cut in such a way that it could be assembled into a \(3-D\) shape anytime.
 
Example:
Let us look at the net of a cube.
 
1235_17.svg
 
 
Let us also look at the net of a cylinder.
 
1235_18.svg