How is the Course of becoming a Cardiologist done

Um please please anyone who's becoming or have already become or have some of your friends or family become a doctor can you please tell me how the things are done? I wanna plan things out before hand and get organised instead of panicking in the last moment of it just for your information (just for the sake of letting your understanding to be more better) I'm a 3rd year in high school (grade 11) and I'm a IGCSE student I wanna know what is the thing I should start doing right after graduating from high school so that I don't waste much time

thank you

i am currently in the US and is going to a foreign university...i have yet decided to be a nurse doctor study medicine be a surgene etc...all i know...the thing is once you enter any field involving the human body you will have to learn everything or mostly everything about the hhuman body a cardiologist does not only have to learn the heart lungs etc(cardiology) i have began my own studies reading books on all medical fields to get the scope of things i suggest you get to it as well...however..decide if that is what you want because you would just be wasting yur time gwtting ready for something you may not want to do later in the future