The standard WordPress block
WordPress needs a small mod_rewrite block — between # BEGIN WordPress and # END WordPress — to route pretty permalinks through index.php. WordPress writes it for you when permalinks are saved, but a lost or emptied .htaccess breaks every URL except the home page. This regenerates it.
Redirects
Force HTTPS and the www / non-www options add canonical redirects above the WordPress block so they run first. Pick one www direction and stick with it — redirect loops usually come from also forcing the opposite elsewhere (a plugin or server config).
Performance & hardening
Caching and gzip add Expires headers and compression for faster repeat visits. Protect wp-config.php, disable directory browsing and block xmlrpc.php are common hardening steps. Only block XML-RPC if nothing you use needs it (some apps and Jetpack features do).
Testing rules
To check how a specific RewriteRule or Redirect behaves against a path, use the .htaccess Tester.