I made a coffee maker for my scene. In Substance Painter my carafe is set up to look like glass. How do I use my opacity texture?
Set the blend mode from Opaque to Translucent.
After you have set it to translucent, you will have to add some more nodes so that it looks like glass 
https://forums.unrealengine/showthread.php?1037-How-do-I-make-realistic-looking-glasshttps://youtube/watch?v=sRQ5z8i_SV8
But when you use glass for one of your objects, it’s recommended to put it on a separate material slot -> otherwise the rest of the mesh is also translucent