I've got a new website which I may update every day and add 2-3 pages per day. If I submit a sitemap now, what do I have to do after I update the website ?
If you update your website and add 2-3 pages, just add these pages also to the sitemap. Googlebot will see it when it fetches the sitemap.
According http://www.sitemaps.org/protocol.php Once you have created the Sitemap file and placed it on your webserver, you need to inform the search engines that support this protocol of its location. You can do this by: submitting it to them via the search engine's submission interface specifying the location in your site's robots.txt file sending an HTTP request
You're only supposed to submit it once, and then they will recrawl it every so often...whichever you set how frequent to recrawl. No need to continuously submit them!
Why is there a resubmit button then? I don't actually think the number of URLs in my sitemap changed in Google until after I resubmitted it even though it downloaded after the new URL was added.
Don't worry that much about the sitemap it is mostly for sites that are not properly structure (interlinked pages) to help the search engines find all of the pages Even with a proper sitemap google might take long time to visit all of them The resubmit button exist in case you drastically change the URLs of your site you don't have to hit that button every time you add a page just include it in the sitemap and google will periodically check your sitemap
I submit a new one after new content is added to my site - about once a month....maybe. Dont think the Sitemap is that important.
Not sure why everyone is constantly resubmitting their sitemaps, you dont need to do it after every new page
Most of the info in this is not correct at all. You don't need to keep resubmitting your sitemap to Google. You can keep your sitemap.xml updated if you want but if the pages are linked the bots will find them.
It is better to update sitemaps whenever you update the site. You should update it periodically atleast weekly.