A site that isn't properly indexed can't rank for anything, which makes confirming your pages are actually in a search engine's index one of the most fundamental DIY checks.
Search Directly for Your Own Site
A simple site-specific search shows you which of your pages a search engine currently has indexed.
Check for Pages That Should Be Indexed but Aren't
Comparing your actual page list against what shows up in that search reveals gaps worth investigating further.
Investigate Why a Page Might Be Missing
A missing page is often explained by a blocking robots rule, a noindex tag, or a lack of any internal links pointing to it.
Next step: Use the SEO Audit to check your site's overall indexing status as part of a fuller diagnostic pass.