Some of the commands more used in modelling are Scale, Rotate e Grab.

It's very useful to know their hotkeys because use only the mouse spend much more time.

To use them, press TAB and change to Object Mode, right-click on the object and you will see it get pink.

Press on the keyboard: S to Scale, R to Rotate or G to Grab.

After, it's only move the mouse to modify the object.