Caching not working. Help!

I installed the WP Super Cache plugin but nothing is happening. Site is still slow. I checked the content tab under settings but no page seems to be cached (except for the homepage). Is there anything to make it work? Please see screenshot here: https://www.dropbox.com/s/neg59cu8e3iee8l/Screen%20Shot%202015-12-02%20at%204.06.58%20PM.png?dl=0
Thank You!

https://ww.wp.xz.cn/plugins/wp-super-cache/