Choose File > New. Once the new document window appears name the document then add width and height.
Create a circle by choosing ellipse tool or by pressing "L". Constrain the proportions by holding the "shift" key. Put color on the circle.
Apply thick stroke to the circle and color it pink ( R=226, G=14, B=65 ). It helps to define the button and gives the button look. Now apply the gradient to the fill. For reference you can see the below image.
NOTE - In gradient fill use the shades of color that you are using in stroke.
Now we have to give the touch of glass in the ellipse. with the help of ellipse tool draw a small oval on the upper half of the first circle. align the both circle. Now apply the same gradient in it.