Obviously, strength comes from increasing your muscles. The best way to increase strength is to work out. But many people don’t know how to work out. Proper form is key to increasing your muscles. If you are new to lifting weights, I highly suggest you ask for help and have someone examine your form. You can seriously injure yourself if you don’t have proper form.
With that said, to build up muscles, you need to lift weights differently than if you would want to become tone. The intensity of your weight lifts will directly affect what your goal is. You can generally follow this idea:
Heavy weights and low repetition e.g. 4~6 repetitions will give you more overall strength in the future than if you were to do moderate weight at moderate repetitions 8~10 repetitions. If you are looking to maintain, you would want lighter weight at higher repetitions 12~14 repetition.
When you work out, you should be doing between 2 to 3 sets of each activity. Therefore, if you are looking to increase your muscles, you should be doing heavy weights at 4~6 repetitions. This means by the end of that 4th and 6th rep, you should be soaked in sweat and having a difficult time lifting those weights. For example, if you typically lift 25 lbs, you should be lifting 10 lbs more. However, make sure you can handle it so you do not severely injure yourself.
At higher weights and lower repetition, your body is essentially ripping your muscle tissues so that it can regenerate and become stronger. When you are working out at lower intensity and lower weights, your muscles don’t tear (as much, at least).