You're new at all this aren't you?
1) Google (XML) Sitemap does not make a sitemap page... there is an other plugin you can try for that called sitemap-generator. Install the plugin, create a page and add the comment the author tells you to add on that page and it'll output a sitemap on that page for you. The google xml file is only meant to guide robots that visit your site so they can do a more exact job.
2) There is a file in your root directory called robots.txt, it's used to give permission to robots for various files and folders. Your file apparently denies all access to robots. You need to change that file. Read up on writing robots.txt and you'll be fine.
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