A Material defines how an object looks in-game, texture, transparency, color, reflectiveness, etc.
Differently from a game object or other assets such as UI elements that you create in the scene, a material is defined in the project and assigned to a game object then go to the Materials folder and with the right click select Create and then Material.
Assign a name to your material, always use names that define the target well in this case “Glass_mat”. The suffix _mat helps me recognize the type immediately.
To create a transparent glass you must first change its rendering mode.
from “Opaque” set it to “Transparent”.
On Albedo, in addition to deciding the color, you can modify the alpha channel of a material. In this case, it will be decisive in defining the transparency of the object to which you assign the material.
Your material is ready, all you have to do is assign the material to the object you want to make similar to a transparent glass.