How do notorious drugs like cocaine affect the mind?

I had friends in college who turned out to be regular meth users and I only found out after graduation. I did not detect anything unusual in their behavior and they told me later on that’s what meth does, gives you a “natural high”.

Much later, while on my first job, a co-worker offered me some cocaine. I told him maybe next time. That was at least 18 years ago. Now I’m wondering what cocaine really does to the brain and what does one feel after taking it?