We've started embracing the world of Composer, the PHP dependency manager. However, it has become one of the biggest pain points reported by Drupal 8 developers. Once using Composer with Drupal, you can no longer simply download zip files to manage your project.
I will go over Composer basics; starting from scratch, and going step-by-step through a full project build.
This will cover many of the topics and steps in a tutorial I've posted on Github. https://github.com/david-hernandez/composer-tutorial
Topics this will include:
Composer.json and composer.lock files
Adding dependencies and development dependencies
Managing version numbers
Scaffolding and scripts
Using the create-project command
This is beginner level information, but one should be familiar with Drupal 8 folder structures and basic command line usage. Familiarity reading JSON files will also help.