The menu links in the left navigation and at the bottom of the home page are not present on the internal pages.
The page Title, Description and Keywords META tags should be different and relevant to each individual page. Along these lines the description tag is reading like the keyword tag. It is recommended that the description be written in complete sentences and composed to draw the attention and interest of the searcher when found in the SE result pages. Also there are two Title tags where only one is needed.
The DOCTYPE is missing, which
http://validator.w3.org/ will explain and help with selecting the correct one to use as well as help to check the code for errors which may cause problems with browser renditions or trip the search engine spiders.
Also, if you check the box for ‘Show Outline’ then you should find at the bottom of the validation result page a reflection of the page out line. The heading tags which reflect the outline can be styled with css to ensure they are being identified as heading tags.
As you will notice when you check the validator, it doesn’t recognize the tags as they are currently being used. The text within the heading tags are weighed by the engines and will give your search engine optimization a boost if you use your keywords with in those tags but consider the visitor reading the tag when composing them so they are not seen as obvious spamming and stuffing of the keywords. These headings should reflect a natural outline of the page content.
Oh, btw, do not be intimidated by the number of errors found on the page, I had hundreds of errors too but it really isn’t as bad as it seems at first. There are many qualified people here willing to answer any questions you may have when trying to correct them!
Wish you well with it!