put this into context that a 14 year old who knows little to basic knowledge about weights would understand.

There r a lot of advanced techniques MLB pitchers use, but when it comes down to it, a lot of the basics will help anybody improve.
Stretching is huge, & very under rated. Any stretch at all for ur shoulder & arm will extend ur flexibility, & allow u to move ur arm more.
Lifting weights will also increase ur power, but be sure to ALWAYS stretch before, after, & even in the middle of lifting. People say weight lifting will decrease flexibility, but that is FALSE if u stretch!
Anything that works ur shoulders, such as push-ups, bench press, using dumbells, will help.
And of course another way is to simply practice. Pitch every other day or so, but be sure not to wear ur arm out. Rest is important. If u have an intense day of pitching practice, u may want to ice ur arm down (to prevent & help any inflammation) that night, & avoid pitching for a few days.
To sum it up: Stretch ur arms a lot. Lift weights, & be sure to stretch before & after. Push ups, bench press, & dumbell weights r simple but very effective ways to build power. Practice pictching often, but be sure to rest ur arm.

basic weight lifting will help your strength but only pitching and improving your mechanics will make you a better pitcher.

Everything that is already been suggested, but do not neglect your legs or your core. Power also comes from hip rotation and PAS leg. Work on explosiveness.

Run more, the lower body is the most important part of the equation

Keep practicing and after you warm up, do some long toss.