nice to meet you. by 'powers' i'm guessing you're referring to Charmed where you can stop time or something. this isn't true. no one has a born power to fly or shoot fireballs or whatever else, this is an invention of hollywood to entertain the masses.
granted, some people are better at certain spells, like healing or love, or paths like herbalism or reiki. how to cast spells, you need to connect with the energy found in nature. there's many methods how, so find the one that works best for you. also, learn what magick can and can't do, basically if it isn't in human nature, it cannot be done. [fly, transform, invisibility] finally, magick isn't a quick fix, or instant, it takes time and you need to put forth effort to attain your goal. if you sit around and do nothing, you'll receive nothing, if you work for your goal, you'll get it much faster.
anyone can join a coven. a coven is like a second family where you learn and grow in the craft. some people don't cast spells and they're still in a coven. each coven is different, but as long as you want to learn/teach you can join a coven. some require certain amount of experience, but normally anyone can join any coven, be a solitary, or start their own.