Ok, what i currently want to do:
I want to create a main screen plugin and in this i need the selected res in the file-system-tab.
In the Plugin-Script itself i can use
get_editor_interface().get_selected_path()
wich works well... i created a signal that fires when the selection is changed, because i couldn't find an existing signal

if (selection != get_editor_interface().get_selected_path()):
		selection = get_editor_interface().get_selected_path()
		emit_signal("selection_changed", selection)

when i connect the signal to self, everything works, but i need this information in my main_screen script...
so now, how to i access the selection-variable in the editorplugin script ... or how the f*** do i connect the signal to my main_screen.gd... because when i connect the signal to the instance it says the function doesn't exists...
core/object.cpp:1236 - Error calling method from signal 'selection_changed': 'Control(main_screen.gd)::_on_selection_changed': Method not found..
..
Signal definition: 'signal selection_changed(new_selection)'
func in main_screen.gd: 'func on_selection_changed(new_selection):'
connection: 'self.connect("selection_changed", main_panel_instance, "on_selection_changed")'
...
may it be that this is the instance of the scene and not the script behind the main_screen? and if so... how to access it... i'm fairly new to godot, so please help me out with this...

    feendrache and found it myself.....
    missed the
    tool
    for the script of the main_screen...
    thx for listening anyway 🙂