Seo-master plugin

I am new to grav(but love it so far) i have just downloaded seo-master plugin,how to i install it please

If you mean https://github.com/Gertt/grav-plugin-seo, it's not in the GPM, and it's likely to be outdated.

Also, there is no readme, so I guess it's not a finished plugin.

You don't need special plugins for SEO in Grav, as everything you need is built-in. You probably need https://github.com/tucho235/grav-plugin-social-meta-tags for social media meta tags, but that's another topic

I'm looking for feedback on a SEO plugin I released few days ago, you can give it a try if you want! https://github.com/paulmassen/grav-plugin-seo