Here are some resources I have found useful (:

Fundamentals:

The Magic of the Terminal: https://missing.csail.mit.edu/

SSH Tunnels: specterops guide to ssh tunnels

Linux

Bandit Wargame: https://overthewire.org/wargames/bandit

Leviathan Wargame: https://overthewire.org/wargames/leviathan

Web

Portswigger Web Academy: https://portswigger.net/web-security

Damn Vulnerable Web App: https://github.com/digininja/DVWA

Web Goat Vulnerable web app: https://owasp.org/www-project-webgoat

Mutillidae Vulnerable web app: https://github.com/webpwnized/mutillidae

Podcasts

Black Hills Information Security: https://www.youtube.com/c/BlackHillsInformationSecurity/featured

Security Weekly: https://www.youtube.com/user/SecurityWeeklyTV

Metasploit

Metasploit Unleashed Class: https://www.offensive-security.com/metasploit-unleashed

Metasploitable vulnerable target: https://github.com/rapid7/metasploitable3

Challlenges

HackTheBox: https://www.hackthebox.eu

TryHackMe: https://tryhackme.com

CTFs: https://gitlab.com/r00k/ctf-resources

Cheat Sheets:

SSH pivoting: https://sleepy-student.co/blog/ssh-tunnels

Windows File Upload: https://sleepy-student.co/blog/uploading-files-to-windows-machines

Linux: https://sleepy-student.co/blog/linux-cheat-sheet