I can't compile

I loaded Arduino and teensy extensions - followed detailed instructions
I have Marlin V1 firmware. The files r in the marlin folder.
when I open Marlin.ino in Arduino it opens the file and I can look at the configuration.h file and everything is good until I clk Verify/compile.

Then it can't find Arduino.h - which of course is NOT in the Marlin folder.

Then it can't find a bunch of other files which are in the Arduino\hardware\teensy folder and subfolders
If I copy all the files it can't find into the Marlin folder then I end up with a compile error.

I have been told that I should under no circumstance move/copy these files to the Marlin folder, but that is the only way to get past these errors.

Where can I find details to solve this issue and get my f/w compiled?

This is the code:

#ifndef CORE_TEENSY
#define CORE_TEENSY
#if defined(USB_SERIAL)
#include "../usb_serial/core_id.h"

This is the error:

In file included from /wiring.h:32,
from /wiring_private.h:33,
from pins_teensy.c:28:
core_id.h:4: error: ../usb_serial/core_id.h: No such file or directory
In file included from pins_teensy.c:30:
usb_private.h:2: error: ../usb_serial/usb_private.h: No such file or directory
pins_teensy.c: In function 'init_Teensyduino_internal':
pins_teensy.c:86: warning: implicit declaration of function 'usb_init'

So where is that ambiguous path pointing?

../usb_serial/usb_private.h

Are you using a Teensy or an Arduino?
If you're using a Teensy you should ask this in the Teensy forum: PJRC (Teensy) Forum
If you're using an Arduino, why does that snippet force CORE_TEENSY to be defined?
What is Marlin?

Pete