How do I spawn a model with a button on a surface gui?

I'm not sure 100% what your question means, but your going to need to use Instance.new in order to spawn the objects.

The API Instance.new has two arguments. The first being the object, and the second (optional) argument is the Parent.

Instance.new(object, parent)

Thus, you can do something similar to this in order to create the objects you need to create:

-- Declaring variables
local part = Instance.new('Part')
local surfacegui = Instance.new('SurfaceGui', part)
local frame = Instance.new('Frame', surfacegui)

--Editing created instances
part.Size = Vector3.new(5, 5, 5)
surfacegui.CanvasSize = Vector2.new(100, 100)
frame.BackgroundColor3 = Color3.new(80/255, 60/255, 100/255)