in the US after med school you do an additional 3-7 years of post-grad training called residency depending on your specialty of choice.
Generalist/medicine is typically 3 years. Surgery fields are longer. Pay is just slightly better than minimum wage.
After residency you can do fellowships to sub-specialize further in your field (typically another 1-2 years). This is where someone would become a cardiologist, GI specialist, etc.
I did intern year in internal medicine. I failed to match to one of those cushy transitional years and I had to scramble in to an IM spot…fortunately the new program director at my institution had mistakenly not ticked the box to roll unfilled neurology intern year spots into the main match…so it was a nod and a wink before the official handshake the moment the scramble opened. It was chaos for them as they had 2 of the 89 unfilled spots in the whole country…but both were filled essentially instantly.
I matched in what was then a competitive specialty at a top program but failed at the easy part :)
