Meta Keywords Attribute: A series of keywords you deem relevant to the page in question.

Title Tag: The title of your page.

Meta Description Attribute: A brief description of the page.

Meta Robots Attribute: An indication to search engine crawlers (robots or "bots") as to what they should do with the page.

Meta Keywords Attribute is antiquated, and you shouldn’t worry about it. Your Meta Robots Attribute is most likely already set to “index/follow”. What you should worry about is your title tag and meta description.