People are always asking or saying how they want to "tone up." I find this annoying, because what does "tone" mean? This a word used to hide the real definition; to lower body fat and increase muscle mass.
How do I lower my body fat? Well the short general answer is have more output than input. Use more calories than you take in. Although the calories you intake also matter; think this doughnut vs these apples. They are both 200 calories, but a very different 200 calories. One gram of protein or carbohydrates is 4 calories, while a gram of fat is 9 calories.
Lifting light weights for 100's of repetition does not lower body fat, it may help build some endurance though. If your goal isn't to build muscular endurance, why train for that? Also you can't target areas for fat loss, the human body doesn't work that way. For the most part, we lose body fat evenly across the whole body. This means doing 100's of crunches won't automatically shed the fat stored around the abdomen, although it will build the muscle under the fat. Same goes for doing dozens and dozens of curls with light weight to lose arm fat; it just doesn't work like that!
Women also tend think weight lifting makes them bulky, if you look at any of the fitness models that have the very athletic look to them, chances are it came with resistance training. Women want a firm and round shaped bottom, but do not want or know how to train for it. Like any good looking muscle, it has to be challenged and stressed; squats are often called the "king of lifts" for a reason.
Squats aren't the only thing you can do to stress or challenge your lower body; lunges, deadlifts and plyometrics are phenomenal exercises to form a nice sculpted figure.
Now we can define "toning up"; more lean body mass, and lower body fat. We also have the method to get those results; resistance training and more energy used than taken in, respectively.