How is this person changing this objects shape?

I was watching this video ( and could not figure out what this guy was doing to the object to change its shape and make it bigger. I anyone could help me by telling me how to do this that would be so awesome. Thanks!

Could you specify?

I am not sure if you mean him re-sizing it or just extruding it.

He is speed modeling an assault rifle using many techniques. To learn them, I recommend this series of tutorials. Number 3 covers modeling.