For example of how the crawling process works in practice, it helps to work with a sample text.  Let’s consider this paragraph:

If you have a winning way with words, you may be interested in learning more about direct mail copywriting.  The field offers powerful writers the opportunity to be free of geographical constraints, to earn passive income, and to pay their bills without having to work a boring nine-to-five job.

In short, direct mail copywriting is a very tempting career option for many writers.

Now, while it is true that you can make a very good living with direct mail copywriting, not every one who enters the field is going to be able to do it full time.

Clients do not come crawling out of the woodwork and run straight for your door.

The successful copywriter has to attract new clients, maintain existing relationships, and consistently deliver copy that converts.

What are some of the words used in this paragraph more than once?

Maybe you chose copywriting, writers, and direct mail.

The web bots would do the same thing on a larger scale.  Thus, if you were looking for information about dog food, and typed “dog food store” into Google, this article would not appear in the search results, because the bots would not consider it relevant.

The phrase ‘dog food store’ does not appear once in the sample text, so the bots would skip over this article when pulling up choices for the search results.

On the other hand, if you were looking for writers for an ad campaign and typed “direct mail copywriter” this article might appear on the first page of your search results.

It used your search words, also known as your “keywords” multiple times, prompting the bots to match you with an article where your desired words appeared more than once.