This would get you the index of the clicked row, starting with one:
$('#thetable').find('tr').click( function(){
alert('You clicked row '+ ($(this).index()+1) );
});<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table id="thetable">
<tr>
<td>1</td><td>1</td><td>1</td>
</tr>
<tr>
<td>2</td><td>2</td><td>2</td>
</tr>
<tr>
<td>3</td><td>3</td><td>3</td>
</tr>
</table>If you want to return the number stored in that first cell of each row:
$('#thetable').find('tr').click( function(){
var row = $(this).find('td:first').text();
alert('You clicked ' + row);
});