Also, what do you think about playing a lot of openings without studying them very much?
not gonna lie, pretty dumb... you really should try to analyze your openings and understand them before playing them. unless you are like 100 rated. then don't worry about studying openings. but players of all levels should try to understand their openings
But, I mean, understanding them, but not knowing all the lines, just the main ideas and the principles of the opening phase. Is that right? Or is it still pretty dumb?
if you are a beginner, understanding the main ideas is key. however, the better you get, the more you'll have to know in terms of exact variations in order to survive. you'll figure it out...
(i've lost many games due to lack of opening knowledge. once you lose a game like that, study! )
My parents just wont buy me a uscf membership, can i still improve by playing online?
yes you can! i would recommend playing lots of games online, since no one really has a chance to play any tournaments anyways. eventually you should get a USCF membership though (only for US people, lol )
Yes, once im 18 my parents wont have control over me