I used to follow the Grateful Dead when the toured. They formed in 1965 in California, and because very popular.  
Ah neat, I'm not too familiar with much of their music. What do you like about them?
Well the band have a very unique style of eclectic fused with rock and psychedlia experimental. They are an experience to watch in concert!
I'm always down for a psychedelic rock experience! How popular are they? Have they sold a lot of records?
yes! They ranked 57th by "Rolling Stone" magazine, so they're are very popular in the rock community.
So for the uninitiated, what are the essential Grateful Dread tracks that I should go put on my Spotify playlist right this instant?
Their album sold more than 35 millions world wide. Honestly anything you find by them is a classic. It be nice to listen to a variety of their music. 
So what's the difference between Grateful Dead and, say, Nirvana, or the Rolling Stones, or Metallica?
Definitely the incorporation of the psychedelic aspect to the rock. They rose to fame in the 60s in the San Francisco Bay area, and they were associated with a lot of drug use.
I think a lot of things in the 60s were associated with heavy drug use, lol. Kinda what that decade was all about, am I right?