Arduino-Teensy programming

Hi, I am looking for someone to help me understand the Arduino and teensy code from a particular project that I found online.

I am an electronics engineer and I have a lot of experience with PLC’s but I a beginner in programming Arduino boards(I have only done basic projects).

So, I found this website https://www.anninrobotics.com/ where they have the instructions to build their robot, they have two versions AR2 and AR3, I am building the AR3 right now and I already downloaded the Arduino and teensy code to their respective chips.

The robot control ARCS will integrate the Arduino and teensy boards to manipulate the robot. Arduino board is programmed for the inputs and outputs and the teensy board is programmed to actually control the robot all together with the ARCS control software.

So basically what I need is to get some quotes for someone that can explain to me the Arduino and teensy code for this project. The code for the two boards are available in the website I just provided above.

The explanation should be very detailed, pictures, drawings, notes, anything that helps to see clearly what the code does. How the code of each board works LINE BY LINE, how the boards communicate to each other, how the libraries from this project actually works.

To summarize I need someone to explain it as basic and easy as possible for a beginner.