how to make your legs stronger without weights?

There are loads of exercises you can do with just body weight that'll improve the muscles in your legs.

For starters:
Squat jumps--do them without weights, or with light dumbbells in either hand once they become overly easy. Simply stand with your feet shoulder width apart, bend at the knee until your quads are parallel to the ground (you can sink further if you like, just make sure to maintain a natural arch in your back), then explode into the air as high as you can from that position. (Hands should be kept by the ears, elbows to the side, as you don't want your arms to aid in the propulsion upward). Start with 3 sets of 10-15 repetitions, and increase as needed as you grow stronger.

Box Jumps--Find a box, a step, a low concrete wall, bleacher, anything that is raised about 1-2 ft off the ground. Place your right foot on the raised platform, and use it to explode upward. On the descent, land with your left foot on the raised platform (use it to control your descent), and your right on the ground. If you do these right, they're tough. Start with 3 sets of 10-12, adjust as necessary.

Wall sits--Exactly like it sounds. Place your back against a wall, and pretend to sit in a chair.....sitting in a real chair doesn't count. Try for intervals of 3 minutes to start, maintain a 90 degree angle from hips, through knees, to floor.

Calf raises--Find a bench, a table, anything about waist high/chest high that won't move when you grab onto it. Start with your right foot on the floor and your left off the floor (holding it behind you or in front, whichever works, so long as it's not in contact with the floor, and not being held up by something else). Hold onto whatever you're using as a brace with your right hand, and do a one-legged calf raise with your right leg. Use the support your holding on to to ensure that you complete the calf raise all the way up until you're on your toes. Alternate legs and repeat. Do 3-4 sets of 12-15.

Lunges--Place your hands on your head or let them hang loosely by your sides. Step out with your left leg and sink into a lunge. You should make a 90 degree angle between your lower leg and your thigh, thigh parallel to floor. The back leg should make a similar (although obviously reversed) 90 degree angle. Pause at the bottom of the lunge. Then push off your left leg to stand up again, and then repeat with the right leg. Do 3 sets of 8-12 for either leg, waiting about a minute in between sets.

That should get you started.

Also, make sure you're consuming enough protein, otherwise you'll build up more lactic acid than strength and muscle. Easy way to tell? If you're miserably sore, you a) aren't getting enough protein, and b) probably didn't stretch well afterwards. Do both, and you'll be on your way.

(note about the sore bit, if you're a little sore the first few times you try it, no big deal. In fact that's normal, and good. It's the extreme, I-can't-move type of soreness I was referencing above)

Edited to add--all of the exercises save the calf raise work all of the muscles in your legs: quads, calves, glutes, hamstrings.

 

Can I just say these are ridiculously hard!!!!!!
You can actually feel the lactic acid building up throughout, we all done it in my P.E. class and your legs literally begin to shake after a while.

Have fun!

 

Squats man those hurt at the begining but man they help out at the end

 

Add to that list running stadium steps. Great strength builder for the whole leg.

 

this one is the toughest for me....I do this everyother day, lunge walking 30 yards 8 times and I don't take a break; my legs feel numb by the time I finish

 

Make sure that when you guys are doing lunges that you're doing it slowly and deliberately. Don't use your momentum to lift yourself up or to take the next step, or you will start putting other muscle groups into the mix, and that won't help that much.

 

as someone else said above wall sits are the bomb, to improve your speed, and your kicking power, i started out doing them with nothing, and now do them with 50 pounds on my legs.

 

No one mentioned sissy squats. Even though the name sounds dumb, these can leave your legs burning for days. Grab some sort of pole if you have one in your basement or anything to support the house, put your feet close to the pole and lean all the back. Do squats from this position until you can't get up anymore. It works, trust me.