MyBB Community Forums

I am talking about this one
http://mods.mybb.com/view/google-seo

So many text files in there but no instruction.

I have no idea how to install it.

By the way, is it the best tool for MyBB forum?

Google SEO is one of the most well documented plugins available for MyBB. Check the download again, full installation instructions are included.

I am sorry, I am totally new to this. I checked every single .txt file in there, and I haven't seen anything telling me how to install it.

There are total 10 .txt files, and 2 .php files.
Could you please tell me exactly which file contains the installation instructions?

Try looking here - all the documentation is available on a single page: https://github.com/frostschutz/google-se...installing

From INSTALL.txt

Quote:Google SEO README
-----------------

The documentation for this plugin can be found in:

inc/plugins/google_seo.html

Please read this documentation very carefully.

Thank you.

Basically:
Upload the plugin files
Edit the htaccess file in the download to suit your forum and domain
Upload the htaccess file to your forum root, save it there as .htaccess
Activate the plugin in the ACP, check for any errors listed.