The object in 8-ball is that you have to Be the first to get all of your balls in and the 8-ball at the end. You and your opponent switch turns every time someone hits unless someone makes one of their balls in. To start, decide who breaks. Then the person who breaks either gets one in or they don't. If they get one in then they are that style of ball (stripes or solids). If you get the 8-ball in on the break then you automatically win, However, if you scratch on the break you lose.
The object in nine ball is to get the nine ball in first by hitting all of the other balls in in numerical order. 9 ball is played with--yep you guessed it--nine balls. The racking is different from 8 ball. if you chain a ball with the nine ball and make the nine ball in then you win, but you have to hit the balls in numerical order.