Unwrapping is when you take for example a cube and flatten it out so you can see all the 6 faces so you can paint them. Obviously it's a bit more complex when you're dealing with around 1000 faces.
The image on the left is before texturing, on the right after texturing. It takes a hell of a long time to get all the faces in the right places to make it easy to paint too. On top of this you can place faces on top of other faces so when you paint it you're painting 2 faces at the same time, this is handy for symetrical stuff, for example the wings and the sides, both sides and both wings are sat on top of one another so both are painted by the same bit (if that makes sense)
The image on the left is before texturing, on the right after texturing. It takes a hell of a long time to get all the faces in the right places to make it easy to paint too. On top of this you can place faces on top of other faces so when you paint it you're painting 2 faces at the same time, this is handy for symetrical stuff, for example the wings and the sides, both sides and both wings are sat on top of one another so both are painted by the same bit (if that makes sense)