How do you paint glass?
I don't believe you need to understand all the physics involved with light, reflection, refraction, absorption, bounce, fall off, kelvins, or watts. But you do need to observe carefully and not let your brain override what you see.
Notice and paint the oddities, squiggles, and stripes. Don't miss the dark passages next to the glistening light. Taken together, these are the things that we perceive to be glass. Maybe we don't understand them but we need to believe they are there and paint them.
Paint carefully, section by section. You're creating a miniature abstract painting that will turn into glass. Don't sweat it if you get a little lost or leave out a few strange shapes. No one will know. Step up to the challenge and practice, practice, practice!