Quads are an important muscle to build, because other than your mouth (j/k), it's the biggest muscle in your body.
For a true beginner, the first exercise that I would recommend are lunges. There are two ways to do them, the first way in the picture being the easiest, and the second being more difficult. You don't need weights to start, but as you get better you will want to add them to your routine.
The first way is you just go up and down up and down, focusing on one leg at a time. Do not rest on your knee as it gets close to the floor, at most let it lightly tap the floor, but I don't let mine touch. Make sure your front leg thigh is parallel to the floor during the downward rep as shown in the picture.
Now a harder way is as follows....same principle, but you are taking a large step forward, and then pushing back to the starting position. This one is much better for your legs, and will work your hamstrings and calves substantially more than the first type of lunge.
Leg Press is next! There are two types of leg press machines, one uses free-weight plates, and the other has the stacked numbered weights with the metal peg you put in the hole to choose your weight.
This is the one below utilizes free weight plates for your weight. Make sure you start of with no weight to get your form down. There is a safety feature to this machine that prevents the weights from crashing down towards you. First you push the weights up, then you turn handles on the side of the machine to remove the safety, then you can bring the weights down. You may want to consult a trainer at your gym before attempting this for the first time. On the return part of the repetition, your legs do not need to go any less than a 90 degree angle as shown in this picture, and on the upstroke straighten your legs, but do not lock your knees. This is important. This workout is great for your quads and hamstrings. If you want, you can vary your foot position. Move your feet higher on the board to work your hamstrings more, or point your toes outward to work the insides of your thighs more.
Leg press machines come in all shapes and sizes. These next ones do not require a spotter or have safety mechanisms to fight through...
more quad exercises to come...but I have to jump on a plane
