What does Marijuana do to you?

As in, when you smoke marijuana, what happens to you afterwards exactly and why? How does it work? I would love a play by play informed answer. I’m talking psychological and physiological. But not just what happens, also why.
I’m curious as to what it does to the body exactly?

I smoked it once and my heart was pounding for an hour an a half while I was high. Either I was paranoid (so it was psychological) or it was just physiological from the marijuana, what do you think?

So pretty much I want to know all the different things marijuana does to someone, the facts. and how it works and why, I know I must sound like a broken record but I just want to make sure people know what I mean .