How do you change the opacity of a layer on GIMP?

I've been trying for the past hour. Does anyone know how?How do you change the opacity of a layer on GIMP?
In the layers tab under the control, ';mode';, there is a opacity slider where you can set it. Also check if you have the right layer selected if you have multiple layers.





Here's a page that has a pic to clear up my words:


http://www.ischool.utexas.edu/technology鈥?/a>