I can't see button in unity code example

Example: unity can't see button

Select your canvas, go to the canvas component > Render Mode.
Change it to "Screen space - camera" and add your main camera to the section
below that. Now try to find your buttons somewhere on the screen (Select the 
button from the hierarchy and Press F) and even if it didn't work (it will!),
go to the game view and play with the scale and position of your button until
you can see it.

There is also a possibility that the button is in the back layer.
You can change the order of let's say your background, when you select it
(Sprite renderer > Additional settings > Order in Layer).