Maybe you have never done this

If you have never strength trained and wan to start. Great.
This is a good move for anyone.

You can begin by using your body weight to strengthen the muscles.
An example- Curl your arms up pretending that you are raising a weight. Feel the tension in the arm muscles, don't strain.

Just apply tension and relax, then do it again. After 10 or so repetitions you should start to feel the muscle swell up and maybe tighten a bit.

Do the opposite move, push down be bending from the elbow to tighten the tricep in the back of your arm..

Next push up your arms as if lifting a weight overhead. You should feel this in your shoulders.

These moves will start your training. Later you can replace them with lifting actual weights. Body tension exercises work!
 See information on Charles Atlas. This was from his Dynamic tension routine.