The exercise program you choose depends entirely on your fitness goals. The exercises you will be doing and the approach you take in performing these exercises will depend on whether you wish to gain muscle and strength, tone and lose weight or just stay in shape and be healthy. I will briefly describe a sample exercise program which can be adapted for all people regardless of your age or fitness objectives.
If you are looking to build muscle or strength via a bodybuilding routine, stick to 4-5 sets of 10-12 repetitions. Focus on the positive and negative of each movement of each repetition. Gradually increase the weight as you work out to force your muscles to work. Otherwise your muscles will become programmed, accustomed to the same weight and you will no longer experience any gains. There are many approaches and techniques that can be used in bodybuilding. Experiment and use the best one that fits you. An excellent book about weight training and bodybuilding which discusses many different techniques to working out is the book The Weider System of Bodybuilding
If you are looking to tone or just stay in shape and be healthy, an exercise program combining weight training and a cardiovascular workout is appropriate for you. When you are exercising with weights, 3-4 sets of 12-15 repetitions at a reasonable weight would be appropriate. Combine this with a some cardio exercise 1-2 times a week such as riding an exercise bike or elliptical machine or by joining classes at your gym. It is difficult to show on this web page in great detail exactly what you should be doing.
Here is a sample exercise program that can be modified to fit any person's fitness goals. Remember that you can change the order and incorporate different exercises for each body part on weekly basis. I encourage this to prevent boredom and your body getting used to the same routine.
Before beginning your workout, you should warm up for 5 - 10 minutes on an exercise bike, treadmill or doing some bodyweight exercises. This will prevent you from pulling muscles or injuring yourself. For a cool-down after your workout, you should do some stretching exercises.
These are just general workout guidelines. You may need to consider what ideally suits you best. You may want to add some cardio exercises into the workout days as you wish.