You'll want an
onready var <identifier> = get_node(<path>) to refer to the camera in the player's script, or the player in the camera's script.
You'll also want a vector3 variable, for the offset if you're not using a camera base:
var offset = Vector3(x, y, z)
You can set the projection view of the camera in the camera's properties by the way, but I mainly use perspective so I'm not sure the compromises you will have to make with orthogonal. I used to achieve a pseudo-orthogonal effect by adjusting the rotation of the camera as I wished to emulate the effect.
If this is in the player's script, you will do:
camera.global_transform.origin = global_transform.origin + offset
If this is in the camera's script, you will do:
global_transform.origin = player.global_transform.origin + offset
EDIT: I just found that in the camera's properties is the "H Offset" and "V Offset" variables, so instead of using code to add an offset, you can use that instead if you so choose.