Indexing is the process by which search engines store and organize your pages so they can appear in search results. If a page is not indexed, it cannot rank.
Indexing happens after crawling: Google analyzes a page and adds it to its searchable database. Only indexed pages can appear in results.
Common causes: noindex tags, robots.txt blocks, thin content or crawl issues.
From hours to weeks, depending on site authority and crawl frequency.