For website optimization, are keywords and description in the source code important?

Meta tags are secondary and need to be different for each page. The keyword tag will not help you.
The title tag must contain the important keywords that match the page. The description tag must also use keywords that match the page but also is a good write up on what the page has. Most engines will take the title tag and the description tag and use that in what you see on the organic searches. But, they may also take the first 100 characters of the site, so you need to be sure that is keyword rich as well.

Your meta tags must be used correctly, but is not what will help you get better rankings. they alone will not help but in conjunction with full seo can

<TITLE>use your 3 keyword phrases.no more then 15 words. avoid stop words like 'the', and'</TITLE>
<META NAME="keywords" CONTENT="use your 3 keyword phrases. use comma after each phrase, no space ">
<META NAME="description" CONTENT="be sure to use the 3 keyword phrases. no more then 24 words or less ">
<META NAME="Robot" CONTENT="Index,ALL">
<META NAME="googlebot" CONTENT="index,follow">
<META NAME="Language" CONTENT="en">
<META NAME="Classification" CONTENT="use the best keyword phrase">
<link rel="alternate" type="application/rss+xml" title="ROR" href="your sitemap-name.xml" />

Prominence is best described as how close to the beginning of a specific area in which the keyword appears. A keyword or keyword phrase that appears closer to the top of the page or area may often be considered mildly more relevant.

Keyword placement is better defined as the distance between two keywords or key phrases. You should always keep in mind the importance of keyword and key phrase proximity while carefully writing the content for your website. One powerful technique is to place useful and meaningful text hyperlinks to the internal or external pages of the website. It is my experience that most of these text hyperlinks boost your search engine rankings by a very large factor.

On that very subject, utilization of navigational links across the website will have a powerful impact in gaining priority search engine positioning. Try to incorporate keyword text as part of the link text itself. Having text hyperlinks in each web page adds to the overall link popularity of your website.

Always remember that for maximum search engine optimization and positioning, the actual content of your whole website and the way it was put together will actually determine your search engine positioning and the ranking you will finally achieve. Additionally, various important factors like the formatting of your text, keyword density, keyword proximity, keyword frequency, keyword positioning and finally link popularity are all important and will usually determine if in fact you will be placed above or below your most important competitors.

And never, never keyword stuff. Write correctly, but use your keywords in proper ratio so that it also reads well and makes