WordPress Rocks! but i have messed it up somewhere

First time ever doing a website and i must say i thoroughly enjoyed it, Until now, I have missed something somewhere in the code and i know it.
Allow me to clarify my issues (please dumb your answers down for me as i have never done a website and writing in code is a new interest)

I think i may have missed some steps as the yoast plugin gives me these results:

in open site explorer i get this – No Data Available for this URL

2) when i click the xml sitemap in yoast i get a 404 error

3) this was the density report

https://tools.davidnaylor.co.uk/keyworddensity/index.php?url=https://www.telfordcomputers.co.uk/&keyword=telford+computer+repairs

4) This was the report from the landing page

No meta description has been specified, search engines will display copy from the page instead.
The keyword / phrase telford computer repairs does not appear in the page title.
The keyword doesn’t appear in the first paragraph of the copy, make sure the topic is clear immediately.
The keyword density is 0%, which is a bit low, the keyword was found 0 times.
The images on this page are missing alt tags.
No outbound links appear in this page, consider adding some as appropriate.
The keyword / phrase does not appear in the URL for this page. If you decide to rename the URL be sure to check the old URL 301 redirects to the new one!
The copy scores 53.2 in the Flesch Reading Ease test, which is considered fairly difficult to read. Try to make shorter sentences to improve readability.
The page title contains 37 characters, which is less than the recommended minimum of 40 characters. Use the space to add keyword variations or create compelling call-to-action copy.
No subheading tags (like an H2) appear in the copy.
There are 330 words contained in the body copy, this is greater than the 300 word recommended minimum.

To you guys this may all be obvious but i have missed a step somewhere, I am a 1st timer so be gentle guys

Many Thanks – Steve