1. First thing you want to do is set your canvas dimensions to a workable size.

2. I like to use the Rounded Rectangle Tool, which lets me set how rounded I want the corners of my button to be. In this case, lets leave them at a 10px radius and create your shape.

3. Rasterize the layer. Then with the Marquee Tool select the shape. Create a new layer and go to Select > Modify > Feather… Let’s set the Feathering to 3.

4. Select the Gradient Tool. What you want to do next is then make sure the color white is your foreground color. Apply the white gradient to inside of the shape, once you deselect you will then see a lighting effect you made on the shape.

5. Click on your shape layer. Go to Blending Options > Gradient Overlay and play around with the Opacity and Scaling to give your glass button a more realistic look.

Extra tips: You can always make your button look more realistic, or rather, with more pop by moving your feathered layer down a bit and be sure to use the transforming option to manipulate the width and height. This makes the surface look more polished off.