For example:
You have a table, and it has 4 tds and 2 trs. Table's background color is white. If i click to A td, A td should be red, than if i click to B, B td should be red and A td should be red too. If i click to C than, C should be red and B and A should be red too.

I have something like this. But it isnt good, because when i click again i want to change color back to white.

http://jsfiddle.net/k8UgT/193/

The code i use

<table>

    <tr>

        <td onclick=function()>AAA</td>

        <td onclick=function()>BBB</td>

        <td onclick=function()>CCC</td>

    </tr>

        <tr>

        <td onclick=function()>DDD</td>

        <td onclick=function()>EEE</td>

        <td onclick=function()>FFF</td>

    </tr>

</table>

JS:

$( function() {

  $('td').click( function() {

    $(this).css('background', '#aaa')

  } );

} );