How to sitemap xml

So wether it's wordpress or google blogger an xml sitemap will be used to index the sites is it? So for blogger you can use webmaster tools and just add atom.xml ,,,maxresults=500 and then it will be submitted and wait for it to be indexed by google? For wordpress Get an xml sitemap plugin and it will do this auto? So there's no use for robots since i don't know what it does do i use robots or not as well, and an xml sitemap shoul'd be submitted after the site is optimise

Sitemap will help to crawl your overall site, first you need to create sitemap( you can search google " sitemap generator" and upload it in your site.
After you will create robot.txt file and upload it.
Sitemap and robot are need to your site to be good optimized.

I try to create sitemap on early stages to get good google indexing afap. Just put the sitemap plugin and forget of it.

Create a sitemap of your content pages (e.g. if using WordPress you can use a plugin that will select only those) and noindex tag and category pages. (That way, you won't really need robots.txt alhough it will of course be time well spent learning about it)