List of learning resources, learning/challenge sites, and tools useful for CTF and cybersecurity in general. Please use this knowledge responsibly :)
Challenge sites are websites where you can practice your hacking knowledge in a controlled environment by solving challenges and penetrating machines with vulnerabilities on them. They are a fun and interactive way to learn, and are usually open 24/7 with no time limit.
Hack The Box: https://www.hackthebox.eu/
OverTheWire: https://overthewire.org/wargames/
Tryhackme: https://tryhackme.com/
CTFLearn: https://ctflearn.com/
PicoCTF: https://picoctf.org/
Portswigger Labs: https://portswigger.net/web-security/all-labs
Pwn.college: https://pwn.college/
Nightmare: https://guyinatuxedo.github.io/
ROP Emporium: https://ropemporium.com/
Cryptohack: https://cryptohack.org/
Cryptopals: https://cryptopals.com/
These resources list techniques, tips, and tools useful for when you're working on a particular problem.
HackTricks: https://book.hacktricks.xyz/
Cheatsheet-God: https://github.com/OlivierLaflamme/Cheatsheet-God
PayloadsAllTheThings: https://github.com/swisskyrepo/PayloadsAllTheThings
OWASP Top 10: https://owasp.org/Top10/
GTFOBins: https://gtfobins.github.io/
Cryptobook: https://cryptohack.gitbook.io/cryptobook/
There are plenty of great cybersecurity youtubers out there making videos about various topics in cybersecurity. This is a great way to learn about unfamiliar topics.
John Hammond: https://www.youtube.com/c/JohnHammond010
LiveOverflow: https://www.youtube.com/c/LiveOverflow
Computerphile: https://www.youtube.com/user/Computerphile (Mike Pound's videos are especially recommended)
IppSec: https://www.youtube.com/c/IppSec
Nahamsec: https://www.youtube.com/c/Nahamsec
Stok: https://www.youtube.com/c/STOKfredrik
PwnFunction: https://www.youtube.com/c/PwnFunction
GynvaelEN: https://www.youtube.com/user/GynvaelEN
David Wong: https://www.youtube.com/user/debman3
Nox Populi: https://www.youtube.com/c/NoxPopuli
CryptoClear: https://www.youtube.com/c/CryptoClear