How to check the website is indexed or not in Google?

You can use this code directive in google search by providing site:www.site.com then google will show site pages that are already index in their database.

site:yourdomain.com

There is one way to check the indexing of a website. The way is
site:url. For example
site:https://webhelpforums.net/

For example, your website URL is www.example.com. By using that directive code "site:www.example.com" in the browser or search bar you get your all index pages in the google search result. 

You can type in the Google site:yourwebsite.com and check what pages of your website Google showing, check carefully all the pages and check also their Title & meta description, URLs check your sitemap and match no. of pages Google indexed.

site: is the operator to check whether website is index or not in Google search engine.

by means of the use of a easy browser search query with the so-referred to as "site:" operator and your domain, you may get an approximate number of pages indexed through Google