The values from the button are available in palette 'sensing', right down at the bottom at '... sensor value'.
The value is '1' for an open button and '0' when button pressed. The reason is the connection with a pullup resistor.
Task: Control the LED with the button:
forever if gpio23 sensorvalue == 1 broadcast gpio17off else broadcast gpio17on
Additional idea to spend some time: Build an edge detector for the button.