How to Setup Simple SEO Kewords

Hello there!
I am looking to understand the keyword ability under "manage pages" on the Editor.
Can I just type in any string of words, and Google analytics will pick them up and map them? Do they need to be sentences, separated by commas, or? Is there a limit? Also, where do things typed in the "description" box show up, and what is their use?

Thank you,
Heidi
Site reference: ranchwildfire.com