Basic Push Button

First make a new image 200x200 pixels, then create a new layer.

Use the elliptical marquee tool to make a circle selection (Hold down shift key to draw a perfect circle)

Press D and X to reset the background color to black and foreground white. Then use the Radial Gradient to fill the circle from top left to bottom right like the picture on the left.

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Now go to Select>Modify>Contract, enter 6 for pixels Then go to Edit>Transform>Rotate 180

Go to Select>Modify>Contract, this time enter 2 for pixels

Then go to Edit>Transform>Rotate 180

To color your button, Go to Image > Adjust >Hue, check the "colorize" box and adjust anything there untill you like.

Apply any layer effects you like, for example drop shadow, bevel & emboss...etc