The code got cut-off in your title there... but <a href is the html code for making a click able link. <a href="http://yourpage.com/page.php ">Description of link to click on</a>
That's how a normal link would look. The apostrophe's ( ' ) are just used to let the server know that anything between the two ( ' ) is to be considered the website address (you can use ' or " but I prefer ")
If I'm not mistaken the brackets { } are to let the web server know that between that is php code, not just normal HTML.
Your problem of finding out what the $URL_Login variable is going to be impossible unless it is your PHP file. When a web server loads a php file it normally converts all of this information into html code... normally you never see any of the php code or variables unless that web server does not have php installed.

If you've found a website and this is showing instead of the actual link then you can't do anything about it.

If you have the original php file in your possession do a search in that file for $URL_Login or search for the word include.. sometimes in php files people have all the variables in another file and they include it which loads all that information into the page.

(This is starting to go a little bit out of a way I can explain it... if it doesn't make sense I'm sure someone else can help me explain in a more simple manner)