Ok, lets say you got a rectangular image with a logo that you want to make into a button.
First you might want to select you Elliptical Marquee tool
And draw an ellipse around it
Then make a new layer via copy.
Now you could turn off your original layer and that'll leave you with rounded button and transparent corners (assuming you want transparent corners)
Then for your active layer, go and double-click in this area of layers palette
That will give you the Layer Styles dialog
Just start playing with the layer styles. Turn things on and off, adjust things, see what all the various effects do. You can go with some of the preset styles of just make your own. In my example here, I just used a simple black Stroke around the border, some bevel to give it a 3D look, and some texture to the surface of the button. And that's it. About 2 minutes from square logo image to round button image.
Linear Mode
