How do I install the MagMi for Magento 2 extension?

There is not install for magmi just Copy magmi in main folder

/magmi

and just the following your url you will be able to access the magmi

http://installmagentourl/magmi/web/magmi.php and use default user: magmi paswd: magmi

You are good to go..

One thing more

go to magmi/inc/magmi_engine.php replace the one 511 line and replace else code and add you credential

else {
                $host = $this->getProp("DATABASE", "host", "localhost");
                $dbname = $this->getProp("DATABASE", "dbname", "magento");
                $user = $this->getProp("DATABASE", "user",'root');
                $pass = $this->getProp("DATABASE", "password",'root');
                $port = $this->getProp("DATABASE", "port", "3306");
            }