Step 1: Download Tor (vidalia bundle) from here orfrom the original author's website i.e. https://www.torproject.org/download/download.html.en
Step 2: Install Vidalia as a full installation and open Vidalia Control Pannel.
Note: If you are not using any proxy then go directly to step 6.
Step 3: Open Settings of Vidalia Control Panel.
Step 4: Click on Network tab.
Step 5: If you are behind a proxy tick the check box "I use a proxy to access the internet" and enter your proxy settings here and hit OK.
Step 6: Now open up your Internet browser and change your proxy to 127.0.0.1 and port to 8118. Use this proxy for all protocols and save.
Step 7: Now you are good to go browsing any blocked website by your school, college or office or anything such.
Note: Make sure that vidalia is running so you can actually access the internet through TOR Network.If not, then first start Vidalia by navigating to start menu and all that.