Use your rectangle tool to make any shape that you would like to make into a metal button. I applied a roundness of 100 to mine, but you can do whatever suits you.

In the properties window, click on the dropdown menu entitled "solid" and change it to Gradient > Linear

Click on the colored box in your properties tab to change the color of your gradient. Click on the color icons to the left and right, changing the left to a light gray, and the right to a dark gray.

You will see two anchor points added to your rectangle, to change the direction of the gradient, drag the points to the position shown below.

In the properties window, click the + sign to add a filter. Choose Shadow and Glow > Drop Shadow.

You should have something similar to mine

Now lets make this look a little more metallic. Go back to your gradient colors by clicking on the colored box in your properties window next to the paint bucket symbol. Place your mouse below the gradient, and you will see a + sign appear. Click here allows you to add a new gradient point. Click to add, and change the color to white. Drag your new icon to the position shown below, or to a place that gives you a nice metallic. shine on your button.

Change the border to 1 pixel, and the color to dark gray.

Click on your rectangle tool again, and make a new shape. Make it slightly smaller than your previous rectangle, similar to mine.

Change the gradient anchor points, as we did earlier, this time place the white color towards the bottom.This contrast will help give the illusion of depth.

Add some text and your all done, here is how mine turned out.