You just need to submit the sitemap just once. Google will be pinged by the sitemap file itself as soon as you publish new content.
You need to have at least 10 well-written articles before asking search engines to crawl and index your blog. You can submit anytime you want but to give a better impression, submit sitemap when you have content on your blog. Submitting a sitemap with no posts would surely look weird!

It is collection of web page so when your have create many pages then you submit XML sitemap your website.

You just need to submit the sitemap just once. Google will be pinged by the sitemap file itself as soon as you publish new content.
You need to have at least 10 well-written articles before asking search engines to crawl and index your blog. You can submit anytime you want but to give a better impression, submit sitemap when you have content on your blog. Submitting a sitemap with no posts would surely look weird!