When you put a website online, search engines will need to send out “bots” and “crawlers” to find keywords that tell them what your page is about. Then it creates a tag for the web page and files it in the search engine’s database. This process is called Web Indexing.
So the spider / crawlers / bots (HTML & text reading software) are sent out, crawls every web page out there, then stores it in the Web Index. Then based on Google ranking algorithms it will then match user queries with results.
When you create your website, you also want those crawlers to crawl your web pages, tag them, then Index them.

But how does Google do Web Indexing? Check out the video below from Google.
In conclusion, you want to make sure that the search engine can match you together with the users and their queries. And as ‘Keywords’ are what spiders / crawlers / bots look for, it is then clear of the importance of Drawing up your SEO keywords as an important step in getting your website accessible, indexable, and searchable by keyword – to match user queries, and get user / buyers to your webpage. Also have a look at how to build tackle your keywords with SEO Keyword Research 101
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