How to properly run proxy on raspberry?

Question

Debian

I don’t understand much about setting up a proxy, so I turn to knowledgeable people :)

Hardware: There is a Raspberry pi3 (Raspbian / Debian) with a USB modem glued to it via (ppp0), Raspberry itself is connected via patchcord to a WIFI router with home Internet. I use VNS to control my Raspberry. If you turn off the Internet from the modem, your home Internet is automatically connected. Internet on a modem and home without a static IP.

Task: Raise a mobile proxy on Raspberry to access it from the Internet, to promote Instagram (we block mobile traffic of Instagram less).

I do everything according to this instruction

. I can't figure out how to fill in the configuration file correctly.
sudo nano /etc/3proxy/3proxy.cfg

Specifically with the fields:
nserver
external
internal

Help, please, to understand.

Answer 1

100500 instructions to google
# Specify the DNS servers
used nserver 8.8.8.8
# external interface for outgoing connections
external 100.100.100.100
# internal interface on which we will expect requests from clients
internal 100.100.100.100