Do you want to get stronger? Do you want to improve your physical fitness?
But are you afraid you'll get to bulky and muscular if you lift weights?
Many women think that if they pick up a weight their going to look too muscular and all they want to do is "tone" so they say, "I'll just stick to body weight exercises.."
There's no such thing as "toning." Essentially, toning means muscle growth. Your skin doesn't just somehow get tighter, your cellulite doesn't somehow just disappear. It's called hypertrophy or building muscle and the overload principal is a good way to do it!
OVERLOAD PRINCIPAL: it's pretty simple really.
Your body adapts to the stresses that you place on it. The more stress you place on your body, the more you become capable of doing.
Weightlifting for example causes physiological changes in your muscle when the weight is heavier than the body is use to. The next time you lift that heavy weight, your body will have adapted to more efficiently handle the stress. By overloading your body with more stress than it can handle, you're making yourself stronger.
For more advanced weight lifters that keep track of their max reps here's a chart for you:
Goal: % rep max Repetitions
Strength >85 <6
Hypertrophy 70-85 6-12
Endurance 60-70 >12
This means that if to gain strength you should be lifting more than 85% of your max with less than 6 repetitions.
Do note, you don't want to do too much at once. Increase your workload from your previous workout, but do it in small increments (aka: be smart). Small increases over time will be large adaptions in the long run. Small steps at a time, but always overload!