Can anyone give me the site from where I can download the software for plotting all kinds of graphs?
There's Graphmatica for Windows. It's shareware, but I understand it is free for those who really can't afford even that. Perhaps another way of asking for a donation for the effort. It's a great 2D program by the way.
The Apple iMac has "Grapher" bundled with a ton of other useful software as part of the package.