First: Open this line.
LoadModule expires_module modules/mod_expires.so
Second: Add this segment.
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/html "now plus 5 minutes"
ExpiresByType text/css "now plus 2 months"
ExpiresByType text/js "now plus 2 days"
ExpiresByType image/gif "now plus 1 years"
ExpiresByType image/jpeg "access plus 1 years"
ExpiresByType image/bmp "access plus 1 years"
ExpiresByType image/x-icon "access plus 1 years"
ExpiresByType image/png "access plus 1 years"
</IfModule>
Third: Reboot apache.
ExpiresDefault command:
ExpiresDefault "<base> [plus] {<num> <type>}*"
"base" can be set as access, now, modification.
"plus" is keywords of the command.
"num" stands for value.
"type" can be set as years, months, weeks, days, hours, minutes, seconds.