To install KeyCAPTCHA to your q2a site you should:

1. Copy directory keycaptcha-captcha to qa-plugin folder of your Q2A site.
2. Register at keycaptcha.com and add your site to sitelist with CMS type, for example, MyBB
3. Edit KeyCAPTCHA plugin settings and paste your Private Key from keycaptcha.com account>site list>installation instruction
4. Change captcha type in "Spam" settings of your site to KeyCAPTCHA That's all!