How do I add the htaccess code to solve the gtmetrix.com "The following cacheable resources hav

I am trying to speed up my slow WP multisite. I put in WP Super Cache and Autoptimize, and amazingly the site still runs. But I think there is supposed to be some additional htaccess code, that needs to go *someplace* in htaccess, to set future expiration dates. WP Super Cache generated a bunch of new htaccess code, which didn’t break the site. I think I need to add something like this:

## 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 text/x-javascript “access 1 month”

ExpiresByType application/x-shockwave-flash “access 1 month”

ExpiresByType image/x-icon “access 1 year”

ExpiresDefault “access 7 days”

</IfModule>

## EXPIRES CACHING ##

Is this right, and where do I put it? At the end, after the supercashe, and after the WordPress? Within the WordPress?

Thanks