What is a website index?
A website index is a list of all webpages that a search engine knows about. If your web content is not indexed by Google, it won't appear on a Search Engine Results Page (SERP) when users search in Google.
How do I know if my website is indexed?
The easiest way to see if your website is in the Google index is to search Google for "site:yourwebsite.com". The search results should contain all your web content that you expect to be indexed.
For more advanced insight into how Google has indexed your website, use Google Webmaster Tools.