At the top of your Pinterest page you will see a header, with the word Add, if you click on that you will see the following window:
To add a link, just hover over add a pin,
that will open the following window:
just type or past the link to the site you would like to pin, you'll see the next window, where you can decide where to pin your image:
Then you can give your pin a good description, which will encourage others to repin your pin.
Uploading a Pin
You can also click on the Add button and you will be able to hover over Upload a Pin:
This will allow you to upload an image from your computer. Again, you will see the following window:
just type or past the link to the site you would like to pin, you'll see the next window, where you can decide where to pin your image:
Then you can give your pin a good description, which will encourage others to repin your pin.