The three concepts students should understand are:

Crawling → Indexing → Ranking

Crawling

Search engines use automated programs, commonly called crawlers, to discover pages and follow links.

Indexing

After discovering a page, the search engine analyzes and stores information about it in its index.

Ranking

When someone performs a search, the search engine determines which indexed results are most relevant and useful for that query.

Important distinction

Getting a page indexed does not guarantee that it will rank highly.