How do I create a transparent glass cup in OpenGL ES / OpenGL?
Getting something that looks very close to the associated image will be very tricky (the handle is not the tricky part). If this is a tutorial project, I would suggest starting less. Coarser approximations would be a better starting point.
You can easily render a semi-transparent object in OpenGL ES. The OpenGL feature you want is Alpha Blending. It won't help you get close to your glass. http://www.opengl.org/resources/faq/technical/transparency.htm
The basic level of replication for this object will be to use a hand-drawn gray texture that looks like internal refractions and paint it on a camera-facing sprite with partial transparency. Then make a regular high opacity bowl model with a little ambient and diffuse lighting and a lot of specular lighting to make it look shiny.
The effect of multiple reflections on a rounded glass object is much more complex. Especially if you want it to look convincing when there is something other than a blank background behind the cup. This is fairly easy to do in raytracer, but not in a rasterizer like OpenGL. Take a look at Caustics. Methods exist to approximate this effect, but they are not beginners. According to this, GLUT has some examples if you are serious about it. http://www.opengl.org/resources/faq/technical/lights.htm
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I know this post is over a year old, but I came across this post on the internet that might help. (Its Russian or whatever, use google translate to change it to English)
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With programmable shaders, you can create pleasing glass effects such as reflection combined with refraction. OpenGL ES 2.0 has programmable shaders, but OpenGL ES 1.X does not.
A good example of glass with OpenGL ES 2.0 comes with AMD RenderMonkey (free). Download here and take a look at glass examples.
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