Step 1. Lets create a new document, lets make it 200px x 200px for arguments sake.
First up we're going to create the basic shape of the icon. So lets grab the 
Rounded Rectangle Tool (U). Make sure that your radius is 12px, and make a nice perfect square in the middle. NOTE: Hold shift while dragging out your square to ensure all sides stay equal. Name this layer "base".
Step 2. Right click on layer "base", and select Blending Options. Apply the following settings:
It should look something like this:
Step 3. Now onto our text. Choose a font which is Sans Serif (One that doesn't have those fanny lines on it), i chose to use a font called "Segoe UI". If you do not have this font, find something which closely resembles the Photoshop font. I have attached the font at the bottom for download.
Once you've chosen your font, select the 
Type Tool(T), and click on the icon base shape. Type in "Ps". Try to center it as much as possible.
Now all we need is a simple drop shadow on the text. Right click on the "Ps" layer and select Blending Options. Apply the following settings:
It will cause this:
Step 4. Lets make the icon a little more glossy and modern. While holding Ctrl click on the thumbnail of the "base" layer. This should create a selection around the shape of the base of the icon. Create a new layer (Ctrl + Alt + Shift + N), and call it "highlights", click and drag the highlights layer so that it sits below the Ps layer, our text layer.
Now select your Brush Tool(B), and make sure that your foreground colour "#4aaee8".
Now while the selection around the base is still active, and you have your highlights layer selected, create two dots on the top left corner and the bottom right corner, like so:
Turn down the layer opacity to 50%. Press Ctrl+D to deselect your selection.
Step 5. Next step of our glossy transformation.
Click on the Ps layer to highlight it, then create a new layer (Ctrl + Alt + Shift + N), and call it "shine". Now hold Ctrl and click on the thumbnail of the "base" layer, again, this should create a selection around the shape of the base icon.
Now go to Select >> Modify >> Contract..., contract it by 3px. Select your 
Gradient Tool(G), and use a gradient that goes from White to Transparent.
With your gradient tool, create a gradient going from the top left towards the centre, something along the lines of this:
Select your 
Elliptical Marquee Tool(M), and while still on the shine layer, make a selection of the bottom half, then press Delete. This will cut out a hole on the bottom of the shiny bit.
Finished!
And there you have it! Your very own Adobe Photoshop Icon. Play around with colour's and other settings to suit you.
