To go into the link manager, click "Components", then "Web Links", and finally "Links". To get started, click "New" in the upper right hand corner.
The URL box is where you put the address to the page you would like to link to.
In the "Description" text box, write a sentence or two about the site you are linking to. Some sites will have specific text they wish you to use when linking to their site. Include just enough information to give someone who has may have never been to the site, a good idea of what the site is about. For example, if you linked to Google, your description may be, "Google is a powerful search engine that will help you find what you are looking for on the internet."
Where possible it is polite to ask if you may link to their website, and it is best to also ask for a reciprocal link to be placed on their site.