How many reps do I do while weight training?

Our family has purchased a weight bench, but I am unsure of just exactly how many reps to do on each exercise. I am 38, I weight about 175 and I am looking to firm up and lose a few pounds. On the weight bench is the bench press, the lat pull-down, bicep curls and an attachment for leg lifts. How many pounds should I do on each one and how many reps?