Q2A is not a WordPress plugin. It is a standalone application that works with WordPress if you want it to, but works perfectly well as a standalone website.
The notes in the About section here describe how to use WordPress user table instead of Q2A users, and how to amend themes so you can call WordPress functionality.
I have found Question2Answer far superior to any of the forum plugins developed specifically for WordPress. It has better user features, and is easier to integrate with WordPress than many WordPress forum plugins. Also, very good technical support here.