SEO is one of the vital factor for your website to gain visitors. SEO by Yoast make it really easy. I am using this plugin for last 2 years. Before using Yoast i tried many plugins to do SEO with my WP site. But when i started using Yoast it is like "Thank god finally something I found that can reduce my work."
It is really easy to use. Yoast providing you the opportunity to edit the meta-tag, description etc which make your post SEO friendly to the search engine. Instructions are there for your help. You can also check the SEO status of your posts by Yoast. If the SEO sign is green then your post is SEO friendly. If red or yellow, this means there are some problems which you have to solve to make your post SEO friendly. It is very easy.
I am using this plugin and recommend to use this for SEO solution.