Do you just mean a link to the homepage of the blog?

If you're if a widgetised version of WP just insert a Text widget into a sidebar with the code>>

<a href="http://www.yoururl.com">Home</a>

Otherwise use the theme editor and add that HTML into the sidebar.php file at an appropriate place.

No I was not looking for that

I got the solution

if (is_home())
{
echo '<a href=http://www.link.com>link</a>';
}

This code shows a outbound link on homepage only (not on inner pages)

Why would you want a home page link on the home page instead of the inner pages?

There is controversy that Google Dislikes sitewide links..

So Single/Home page links are better. ( but no confirmation of this fact)

I see ... you wanted to place a link only on the homepage of the blog to another site ... not a link to the homepage of the blog