Okay, this is actually very easy. For those who don't know, let me tell you;
--To change the scene:
var user_scene_path = "user://test_scene.tscn"
get_tree().change_scene(user_scene_path)
--To sample the scene:
var user_scene_path = load("user://test_scene.tscn").instance()
add_child(user_scene_path)
I hope I could help.