Okay,everybody sais it is good to submit a sitemap,but I just can't find a clear answer.You must submit the sitemap in www.google.com/webmasters or to include a html sitemap in your website,in the footer?
When people say 'submit a sitemap' they definitely mean submitting one to google webmaster tools. This doesn't mean that adding a sitemap to your site for your users is a bad idea. It's in fact a very good idea.
okay,thank you very much for this answer. Also I would like to know if it is good,for SEO purposes,to have a html sitemap on the website.
Yes. It means more direct internal links to your pages. If a section on a site is not being indexed well, I will usually add links to a deeper level in that section. Works like a charm. I don't mess with XML sitemaps in google webmaster tools myself. But for an online store or something, with lots of generated pages, I probably would. Just to make sure google can distinguish the important pages from the generated fluff.
If you only submit your sitemap to google webmaster account and without adding the html code into your pages, it's useless. They are 2 steps you shall do to make your sitemap work.