One of the ways a website can be shut down is a technique call DDOS (Distributed Denial of Service). The way this works is very simple: If you have enought people loading a particual website over and over again the web server gets overwhelmed and cannot function... effectivly shutting down the website.
You can help do this to the Iranian Government websites by loading the following page:
This will cause the Iranian State Controlled News site to get a page request from your computer ever second... over and over and over. If enough people do this the website will go down.
If you want to REALLY help, load that page in as many browser tabs and brower windows as you can. The more the better.
Once you have a bunch of browser tabs and windows running this... just let it sit there all day long... for days on end.