The process of starting to weight train is somewhat difficult. Many questions like “Which machines should I use?” and “How much weight or how many repetitions?” can seem overwhelming. 
1. The first thing you need to do is figure out your limitations. Fully understand the injuries that you have or have had in the past that may still create a problem today.
2. Next, you need to set a goal. Do you want to reduce body fat, gain weight, increase strength, or increase endurance? Each of these require a modified weight training regimen.
3. Then you need to decide how many days you are willing to dedicate or set aside for weight training. I recommend performing a total body weight training routine three days a week for those who are trying to lose weight and body fat and five days a week for those who are trying to gain weight.
Each day should consist of a max of two muscle groups plus abdominals, for those wanting to gain weight.
For example: on Monday hit chest and back with abs and on Tuesday hit biceps and triceps with abs. The most important thing is to start slow and gradually progress to a heavier weight and more repetitions and sets as the weeks and months roll by.
Also, use machines the first few weeks then progress to cables and free-weights. The machines will control your range of motion and teach your body proper form/technique, while cables and free-weights require muscle ...
