To display a text link:

<a href="URL_OF_SITE_HERE">Displayed Text </a>

To display a text link which opens into a new browser window:

Set target="_blank"

<a href="URL_OF_SITE_HERE" target="_blank">Displayed Text </a>

To make a picture a link:

<a href="URL_OF_SITE_HERE"><img src="URL_OF_IMAGE_HERE"></a>