How important the content regarding text? - Doesn't make sense to me.

The spider is not that smart or is it? - Umm, yes. Google spend billions developing search technology and have some of the most amazing software engineering minds around.

How can the
spider understand what your trying to say and put a relevant to what
your site is understanding your key words are in the text and meta
tags? - Well seeing as META keywords are useless for the Google. They don't use them.

The way the search technology works? I suggest reading here about Google's Algo patents.

KP

The spider (GoogleBot) is quite clever at stripping pages of all the coding tags etc and then retrieving what's left for inclusion within a Datavase. This stored content taken from your page is predominantly the "On Page" visual text. The really clever bit is the Google Algo that then rates that stripped down content according to how relevent it is to the question asked by the Searcher. As KP says the old factors such as KW Tags are now ignored, although I am of the opinion that they are can give a negative loading if stuffed with words and phrases that don't actualy appear on the page. Now there's a thought.

I think the googlebot knows which text it will pick up, as it is design and programmed to do so.