[Plugin: WordPress SEO by Yoast] Alt Tags

I was going through the Source code of my website and noticed the “alt” tags were not taking from the WordPress theme.

I was wondering if there is a way to set this in “Yoast WordPress SEO”

As well is there how to video’s on how to setup Yoast properly?

Thank you,

http://wordpress.org/extend/plugins/wordpress-seo/