These instructions will help create a router from a raspberry pi. The goal is to setup eth0 as LAN and eth1 as WAN. This particular setup works with a raspberry pi B2 and a Huawei E3372 LTE USB stick.
Write 2019-09-26-raspbian-buster-lite.img to a SD-card. Insert the SD-card into the raspberry pi and start it up. Log into the Raspberry Pi and make sure that you can connect to the internet using the LTE USB stick:
$ ping 1.1.1.1
Enter the following command to setup the router:
$ bash -c "$(curl -fsSL raw.githubusercontent.com/brutesque/rpi-router/master/install.sh)"