Right now it has available Sql injection and XSS plugins. Both plugins are designed to catch as many vulnerabilities as we can, it's that why the SQL Injection plugin is a Python port of the great DarkRaver "Sqlibf".
The process is very simple, ProxyStrike runs like a proxy listening in port 8008 by default, so you have to browse the desired web site setting your browser to use ProxyStrike as a proxy, and ProxyStrike will analyze all the paremeters in background mode. For the user is a passive proxy because you won't see any different in the behaviour of the application, but in the background is very active. :)