How do I enter dimentions

 From:  Hammer
3414.1 
I have just downloaded the program and on a whole am excited by the possibilities, but coming from a turbocad background I am use to entering dimentions to size objects, as well as use construction lines that I can space apart for reference. I am not able to find where I can change dimentions after the block is made to rescale it? All help would be appreciated.