Re: new to fly fishing from PA
Welcome to the site! If possible, find someone who teaches casting & get some lessons. That will vastly shorten the learning curve. I learned on my own, but have been fortunate enough to have known some great fly casters & was able to get some help, so that improved my casting, primarily by correcting problems I had.
As far as fly selection, usually that's something we often complicate, particularly since there are so many to choose from. Presentation, which goes back to casting properly is far more important most of the time that the actual fly pattern being used. Since you're fishing for trout in rivers or streams, learn the basic insects & other forage in your area & select a few patterns, sizes & types (dry fly, wet fly, nymph, or streamer) that imitate what the fish might be feeding on, and go from there. If you have a fly shop in your area, that's usually a good place to get advise on patterns and when to use them.
There are a number of flies that are universal in there appeal to various species. Patterns such as the Adam's dry fly, or Hare's Ear Nymphs (or the Gold Ribbed version) work most any place, so they're something you may want to have & something that is a good place to start when there are no hatches to tell you what flies to use. Streamers are another choice, as they imitate baitfish. Something like a Black Nose Dace or Gray Ghost, or perhaps a Zonker are good general purpose flies, and again a good choice to start with. Woolly Buggers are good general purpose flies that can imitate many things.
As you learn, you'll be adding flies & trying different patterns, we all seem to do that, but for now keep it simple, and learn how to cast properly.
Remember, no one likes to be behind the big truck, but that's better than being under it!