This tutorial will teach how to make a very simple, but stylish pressed-in button, in Photoshop using Gradient Tool and Gaussian Blur.

Create a new file of size 100 X 100 pixels. Size and foreground colore don't really matter in this tutorial; it's completely up to you. Set up the background color to white, and foreground to any color you want (I used R:25 G:173 B:14).

Press Ctrl+Shift+N to make a new layer. Then make a circle selection in the middle of the picture using Elliptical Marque Tool() and pressing Shift, to have perfect circle on the left.

Now select Linear Gradient Tool() and draw a gradient from the bottom of the selection to the top. To have a perfect straight line, press Shift while using gradient.

Then make another layer(Ctrl+Shift+N) on top of this one. Go to Selection -> Modify -> Contract and contract the selection by 5 pixels.

Using Linear Gradient Tool() draw a gradient from the top of the big circle to the bottom, pressing Shift in order to have a straight gradient.

Press Ctrl+D to deselect the selection and apply Gaussian Blur (Filter -> Blur -> Gaussian Blur) with Radius equal to 1.5.

OPTIONAL:
Select the layer with the big circle and apply Drop Shadow effect(Layer -> Effects -> Drop Shadow) to it. Also you can apply the Inner Bevel Effect to typography on the button (See the result below).