Google and others have more than just submitting your site to them to be able to discover your site. Chrome for example reports back to google pages you have visited, they also have their own DNS servers 188.8.131.52 which all look out for new pages.
Once google know about a single page that is enough to trigger a complete crawl of your site. If there is also a backlink somewhere, a gmail sent or anything thing else that mentions your site then google can use that and then you will be found.
You could if you want to hurry things along create a search console account and submit a sitemap, but in all honest it wont help much in terms of being found.
Getting your site to rank once found is a whole different story.