What are CityVille links?

CityVille allows you to post links on your Facebook wall. When your friends clicks on one of this links they gain an in-game reward, and let you gain an in-game reward too.
These links aren't illegal and they aren't cheats; CityVille build these links and allows you to use it.
With this in mind it's easy to think how this links are useful, because with them you can gain coins, goods, experience and items such as donuts, zoning permit, or building items.
I'll show you where, in the game, you can have access to these links. In the following images I'll show you how to share a donuts link.

click on Ask for Donuts button

Clicking on the "ask for donut" button will pop-up the following window:

click on copy link location

In this window you have to copy the link location, after that you can go to the main page of this site.

paste the copyied link into the textbox

You have to paste the already copied link into the textbox, and then click on the "send link" button.

click on Send Link button

After clicked to the button, the page will refresh, and your link will appear in the first rows of the tables below the textbox.
Other visitors of the site can now click on your link gaining rewards and let you gain rewards! (To see the gained reward in-game you have to refresh the CityVille game page.)
On the same table you can click on links that could be useful for you: a game page will open up showing you the gained reward.
In the main page of the site there are three tables: the first shows you links about trains, the second shows you links about general rewards and the third table shows you help requested links from other CityVille players. Each table is composed by three columns: the first shows you the time elapsed from when the link was sent, the second column shows you links and the third shows you how many time the link was clicked.
The last thing you should know is that all of the links that can be posted on your Facebook wall, can be posted on this site.
If you found a link that after sending appears in the table as "unknow" send me an email with the link and the expected reward.