it would be the folder structure/file name you are on now. For example, this page's URL is:
http://www.mysite.com/welcome/entertext.php
Then the href for what you have would be:
<a href="entertext.php?click=yes">
or you could do
<a href="/welcome/entertext.php?click=yes">
or you could put in the entire website:
<a href="http://www.mysite.com/welcome/entertext.php?click=yes">