// Node type, node name = create a new one and call the method ()
ColorRect my1 = new ColorRect();
// access the object. object property = create the vector2 (x coord,y coord)
my1.RectPosition = new Vector2(100,150);
// create a vector2 for sixe (x, y)
my1.RectSize = new Vector2(100,200);
// access the colour(British lol) = create the color Color(reg, green, blue, alpha(transparancy))
my1.Color = new Color(1,0,0,1);
// add the new object to the scene
AddChild(my1);
Edit: Added code comments for future reference
C# Resources on godot confuse me as I'm trying to figure out how to 'logically' work backwards from the end node ie ColorRect to find properties in the inheritance chain.