measuring rims/and off set

hi! evryone. how do i go about measuring geo and simular rims,geo's 4x114.3 or i think someone said just 4.25". anyways do I just measure from the end of the lug holes,or measure from the center of each lug hole to the next? and I don't have a clue as to what this (off set) stuff is about? I'm sorry for all these stupid questions,I,m just trying to learn about my 97 1l. (I call it my spam can,spammer) everyone laughs at it ,till I toot my horn at them at the gas station!! If you could help with my questions,I wold greatly appreciate it. thanks,2gooses