1. Make a new picture (CTRL+N) i used the format 477x250 pixels.
2. Make a new layer. Press 'D' to reset the colors.
3. Select the 'Pencil Tool' and set the brushsize to 1 pixel. (look at the image below).
4. You can zoom to make it easier to work. Now draw a box on your image, a tips is to hold shift down when you are drawing a line to make it horizontal/vertical.
Your box should now look something like this: (zoomed 400%)
5. Draw pixels in the corners. (look at the picture below)
6. Click on the 'Eraser Tool' set brush size to 1. Erease the pixels outside your new pixels. (look at the image below)
7. Select a color you like, fill the button with that color. (look at the image below)
8. Select a color that is a little bit lighter than the original color. Draw your image so it looks like the image below.
9. Select a color that is a little bit darker than the original color. Draw your image so it looks like the image below.
10. Doule-click on the layer where your button is to get the blending options window up. Click on 'Drop Shadow', set Distance to 2, OK
11. Write a text inside the button with the 'Horizontal Type Tool', and you are done.
Here is my final result.
More Tutorials: 
