Display block on certain page
If you want more control on this, you can choose the option "Pages on which this PHP code returns TRUE (experts only)" and you can write the following similar code snippet the the box.

&lt;?php
if( arg(0) == 'user' /* &amp;&amp; you may add more conditions here by checking arg(1), arg(2) */) {
    return TRUE; // will display the block
}
return FALSE; // will not display the block
?&gt;


The alternative way is to check the path with regular expression:

&lt;?php
if( preg_match('/^user\/[[:digit:]]$/', current_path()) ) {
    return TRUE; // will display the block
}
return FALSE; // will not display the block
?&gt;


This will show your block only at the path user/*.