Set up the score on The Player Node

Add a CanvasLayer Node as a child of Player

Then add a Label Node as a child of CanvasLayer

Rename the Label to ScoreText

Press F to Focus on it

Set the Text property to Score: 0

This is what is displayed in game

Customise the text

Add a New LabelSetting

Click on the LabelSetting

Change settings as shown

In Player Script

Add an OnReady var to 

set the Label when the Script Loads

Update our add_score function to

 display the increase in score.

use the str function to

combine the integer score with a string.