To install the plugin you need to go to this link here:
There you have a detailed description on how to install the plugin & brief description what the plugin stands for & how it functions.
To get properly arranged with this plugin, you can follow their detailed documentation here:
Set up your forum
To set up your forums on your website, please read carefully this part of their documentation:
Note: For the plugin to work properly you need to check this option on:
Admin Dashboard / Settings / General / Membership
You need to enable the option anyone can register.