How do we notify Google?

You submit your website to google search console

Also you need to verify your website with google search console (a.k.a. webmaster tool) and you need to add xml site maps to google search console. You can do all of that with Yoast plugin and watch on Youtube Yoast step by step tutorial on how to configure plugin and verify your site in google search console and how to add xml site maps to google search console. And on top of that you can add each site manually to google search console in index by google (or crawl like google, I forghot what is exactly name) and ask google to index/crawl your newest post or page.
It is easy to do but it takse around 1 hour to do all of that if you are new to this.

Google search console is very useful to see if everything is ok with your site like 404 errors, 405 errors etc..

And apso you need to have Google Analytics account to monitor how many visitors you have on your site and you can connect google search console account with google analytics account.

Building a website is very easy thing, but other things like google search console, google analytics, cofiguring paypal account and ecommerce/woocommerce setting (if you have e store), adding post, products etc...getting traffic, having and maintaining social accounts and other "fun" things that goes along with having a website are not so easy to do.

Goto the google webmaster tool and submit your site. That will get you listed in a few days.

You have to submit your website on Google Console. Then Google notifies you, about your website.

If you have a Google Search Console account, you can go to Crawl and Fetch as Google, anytime.

Try sending them a postcard.

Just add your website on Google webmaster and submit the sitemap to it and google will index the posts on its own. No need to do some extra tricky work.

Thank you for the information.. Appreciate that

First of all you have to submit your site to google webmaster and also submit the sitmaps and then google notifies you about your website

submit url to google for quick result.