Someone wanted to learn this too, so Grasp built them a personal learning path.
You can keep exploring this one or create a path like this one shaped around you.
Recommended resources
Module 2
Linux Command-Line Essentials
Module 3
Networking Through Hands-On Observation
Module 4
Safe Service Discovery with Nmap
Module 5
How Web Applications Communicate
Module 6
Passwords, Authentication, and Access Control
Module 7
Web Vulnerabilities in Legal Sandboxes
Module 8
Python for Organizing Test Results
Module 9