This is the basic use of the <a> (anchor element) (opens new window) element:

<a href="http://example.com/">Link to example.com</a>

It creates a hyperlink, to the URL http://example.com/ as specified by the href (hypertext reference) attribute, with the anchor text "Link to example.com". It would look something like the following:

Link to example.com (opens new window)

To denote that this link leads to an external website, you can use the external link type:

<a href="http://example.com/" rel="external">example site</a>

You can link to a site that uses a protocol other than HTTP. For example, to link to an FTP site, you can do,

<a href="ftp://example.com/">This could be a link to a FTP site</a>

In this case, the difference is that this anchor tag is requesting that the user's browser connect to example.com using the File Transfer Protocol (FTP) rather than the Hypertext Transfer Protocol (HTTP).

This could be a link to a FTP site