Familiarize yourself with icon creation via two explanatory video tutorials (presented by versed GNOME developers)
Usually, learning is, in the scientific world, performed/achieved by reading books, articles, forum topics, etc, where step-by-step in-depth informations are exposed, informations expressed via text and images.
Nevertheless, learning can be performed via video tutorials, too, where informations are presented in a more familiar user-friendly manner with a video flow that can help the user to immediately grasp various concepts, actions, how-tos, etc, in a relatively small amount of time.
Another built-in quality of video tutorials is the immediacy perceived by the user while searching appropriate tools for a specific "job" (current and/or to be pursued in the future), allowing the seeker to, in a matter of minutes, identify if the visualized tool/app/manner is suitable or not, latter response pushing the user in a separate direction, without spending days reading more complex documents.
The GNOME developers realized and published two video tutorials, aimed at familiarizing the user with creating an actual icon using Inkscape, explanatory method started with the very basic and continued with shaping the concept into a polished icon.
GNOME Design's Jakub Steiner, Adwaita's Garrett LeSage, Barbara Muraus (part of GNOME symbolic icons), Lapo Calamandrei (GNOME themes, GNOME icons) and Hylke Bons (GNOME themes, GNOME icons) explain (in the bellow clips) how to create icons, exposing recommended icon building practices by creating two icons, maps and floppy disk.