First, you need an icon, which should be 100x100px. Of course, if you're using an texture for a blend or banner or layout, it doesn't really matter about the size, as long as the texture fits. For this tutorial, I will be using this icon that I made:

OK, first you need to find an icon gradient. You can use one of mine, or someone else's; it doesn't matter. You need to copy it, and then paste it on top of the icon, like this (below).

Then you go to your layers -blocked- If it isn't open, press CTRL+L, and it should show up. Go to the 'Mode,' and change it to whatever you want. Overlay seems to be the best, though, so that's what I would suggest.

Once you've done this, you're finished! You can go to LAYER - MERGE DOWN, and you're done! Here's my icon with the icon gradient: (below).

You can add brushes, write a little text, or anything else. Hope this helped! If you have any more questions, just neomail me.