Document meta keywords vs template meta same ?

What is the Meta Keyword in the document for ? is this the same as the one that gets put in the header for SEO ?

Does Modx add the meta to our header automatically or do we have to add it ourselves

the way to add meta keywords in the admin area is not easy for newbies.
how to do it exalty, in a simple way for noobs (as i am)
thanks for replies