To enable your browser's caching generally means that you can specify how long browsers should keep images, CSS and JS stored locally. Of course, if you change any of those, the server will tell the visitor's browser to clear that cache. To enable it, add those lines to your .htaccess file:
## EXPIRES CACHING ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType image/jpg "access 1 year"
ExpiresByType image/jpeg "access 1 year"
ExpiresByType image/gif "access 1 year"
ExpiresByType image/png "access 1 year"
ExpiresByType text/css "access 1 month"
ExpiresByType application/pdf "access 1 month"
ExpiresByType application/javascript "access 1 month"
ExpiresByType application/x-javascript "access 1 month"
ExpiresByType application/x-shockwave-flash "access 1 month"
ExpiresByType image/x-icon "access 1 year"
ExpiresByType application/vnd.ms-fontobject "access plus 1 year"
ExpiresByType application/x-font-ttf "access plus 1 year"
ExpiresByType application/x-font-opentype "access plus 1 year"
ExpiresByType application/x-font-woff "access plus 1 year"
ExpiresByType font/ttf "access plus 1 year"
ExpiresByType font/woff "access plus 1 year"
ExpiresByType image/svg+xml "access plus 1 year"
ExpiresDefault "access 7 days"
</IfModule>
## EXPIRES CACHING ##
