I got invited to some group called "Emperors of Chess" a week ago...

I thought to myself, "oh, this is cool..  I am being recruited to a chess team" so I clicked YES...

Now I discover that this group has over 600 members, and my mailbox is being littered with spam every single day from this "group" about tournaments that happen continously...

I don't really get it..  no offense, but this doesn't seem the most logical way to do team chess, with a 600 member team!  The team has no character or personality, its like being part of a mass mailing list in some big multi-national corporation :)

What is the purpose of such groups on chess.com?  I'm very confused..

Those are good questions: what-are-groups 4 and why the hysteria to grow them to the limit?

You can also select which alerts you want to receive on a group by group basis.

Alert Settings

Use the options below to customize when you receive alerts for this group.

•  
  TEAM MATCHES: new team match begins
•  
  VOTE CHESS: new team vote chess match begins
•  
  NOTES: a new post is made to the Group Notes
•  
  NEWS: news item is posted to the group
•  
  FORUMS: new forum topic is created
•  
  PHOTOS: a new photo album is posted

I left "The Emperors of Chess"...

With 700 + members, that group is no more a "group" then is the entire population of a country is a social club..

If that makes sense..

how do you join a group

SHARE -> Groups & Teams.

Scroll through the list, click on a group.

Click on JOIN GROUP.