If you cannot find a mentor...go to you tube (lots of instructionals there). Purchase your gear for the fish that you want to catch! Trying to cast a huge jack streamer with a 5 weight set up will be nothing short of maddening. Many people (myself included) have more than one fly rod for targeting multiple species. When you do get your equipment, find some wide open spaces to practice (a single lot back yard is not big enough, find a park or someplace similar). Get a cheap fly that matches your rod/line, cut off the hook at the bend (trust me....this will prevent the possibility of hooking yourself when getting started). Once you get the basic casting down, head for the water. And remember....don't get discouraged, even us old veterans have bad "fly days"....when it looks like we are trying to cast a wet noodle instead of a fly line...lol.
Research the species you want to catch. For rainbow's, you cannot go wrong with a simple beetle pattern or a small leach pattern. For jack's, the door is open on this one. They will bite on big and small streamers....and even some larger dry flies. Its a case of try almost anything with them. I prefer a larger 4 or 6 inch streamer natural or flashy colors....it's up to the fishes mood. Just remember that you will need a heavier weight line for the big pike streamers (an 8 or 10 weight set up), and for trout, a good 5 or 7 weight.
hope this helps. Others, please chime in to help rdsfishing with the new adventure!