Don't know how to use ScreenTree create_timer in Godot

In the example, the yield keyword is used to tell Godot to suspend execution until it receives an specified signal.

So, if you have code that looks like this:

print("hello")
yield(object, "signal_name")
print("world")

It will print "hello", then after object emits the signal "signal_name", it will continue and print "world".

Let us put create_timer now:

print("hello")
yield(get_tree().create_timer(1.0), "timeout")
print("world")

Understand that get_tree().create_timer(1.0) will return an object. In particular, create_timer returns a SceneTreeTimer. And we will be awaiting for this object to emit a signal called "timeout". In fact the SceneTreeTimer should emit said signal after one second (the time is specified by the 1.0 argument given to create_timer).

If you want to look a little deeper into how yield works, know that it will schedule the code as a continuation of the signal, and return. So Godot can and will execute other things in the mean time. No thread is blocked. This is similar to C# await.

Now, in your code:

func _physics_process(delta):
    yield(get_tree().create_timer(1.0), "timeout")

This will do nothing, then await one second, and afterwards do nothing.

And this is unrelated:

func timeout():
    print("Working")

I don't think that is how the example in the documentation looks like.