example:
you place a wager of $100 on line Over 2.5/3
this means you're bet is split up, one bet of $50 on the Over 2.5, thus if its hits 0, 1, 2 as a total you lose. 3 and up you win.
the other bet also $50 is on the Over 3, so once again a 0, 1, 2 you lose, 3 you push, and 4 and up is a win.
hopefully it makes sense to you.