You are asking how to fully extend your desktop onto two screens. It cannot be done by a trick, you really need (1) either two graphics adapters/cards, or (2) a graphic card that supports two screens (so a card with two output ports).
As the others have mentioned, if you saw somewhere a cable with one connector on one end, and two on the other, it simply means the card has one physical output (probably non-standard) which is actually two in one. But this is probably rare, at least I haven't seen that yet :-)
So, in order to answer properly, we would need to know your hardware platform, and your operation system. If it is a Windows 2000 or newer (which it likely is), and an intel-compatible hardware platform (which it probably is), then you would either need to add a graphics adapter to your pc (different from the type already present), or replace the existing graphics adapter with one that can do dual screen.
For example, if you have a pc with free PCI slots, then adding a PCI graphics adapter would most likely give you the dual screen you want (if your present graphics adapter is not already PCI). Or if you have an empty PCI-Express interface onboard and an on-board VGA connector, you can buy a dual-screen card to plug into the PCI-Express slot, and disable the onboard graphics adapter in the BIOS. These are just two examples, there are quite some possibilities.
With the proper hardware, and two screens attached (some adapters will not be enabled in Windows unless you have a screen attached to it), you will be able to check "Extend My Windows Desktop Onto This Monitor" in Display Properties > Settings"
The best however is to bring your pc or laptop to a computer shop, and ask them for advice. It will make sure you don't end up with the wrong hardware.
