I'm really green about the ears, when it comes to linux.
I would appreciate it if someone can send me a detailed step for step guide on how to install and setup and use Bandwidthd on Ubuntu 11?
Well, unless you need bleeding edge code or are planning on hacking the code yourself a bit, I would suggest starting with sudo apt-get install bandwidthd. That will install it, and set it up to launch when the computer boots. To configure it, IIRC, the config file is in /etc/bandwidthd/bandwidthd.conf, you can edit it via sudo nano /etc/bandwidthd.conf or if you prefer another editor substitute nano for whatever you like (gedit/kate/vim). The config file is pretty straightforward and well enough documented, but let me know if you can't figure it out.