i got a proble in this tutorial here it asks me to download the PSD before starting the tutorial and when i open it just a new window appears with numbers and letters and codes??????????????? whats that what do i do? i will apreciate any help

What you've downloaded is the basis of the gallery thumbnail..
It shows the positioning of the icons you want to make a prewiew of, and of course when you've placed all the icons were you want them, you make the numbers and stuff invisible..

Hope this helps you out a bit...

Right click >> Save As.