Good morrow traveller, this section will provide some links to free platforms where you can train your skills… One of the best platforms to hone your hacking skills.
tryhackme.comGreat up-to-date learning platform. Especially if you are starting on your journey.
PortSwigger AcademyThis is an absolutely excellent material for web application hackers.
cryptohack.orgProbably the best platform to get into cryptography hacking.
linuxjourney.comGreat resource to learn linux and get comfortable with it.
ctftime.orgPrime resource for finding CTF hacking competitions and registering there.

Some additional resources of more varying quality…

BugCrowd UniversityVery nice articles and reading materials.
Intigriti HackademyQuite lightweight and nice articles for main vulnerability categories.
pentesterlab.comOne of the best known hacking platforms, lot of more advanced topics. Monthly subscription. platform to learn network hacking. Access to all labs costs about 10-15$/month.
ctf.hacker101.comNow this one is a ctf program with accompanying training from HackerOne – the bug bounty platform. Their training is mostly video materials, a bit on the boring side, but CTF can be good and has rewards (get invited to private programs). good CTF challenges.
hackingloops.comNice articles, good reading materials.
Crackmes.oneTon of binaries users can upload and reverse engineer/hack. Be careful not to run into malware.

Nice sites that catalogue and resource other pen-testing sources. collection of Pentesting recources
www.redteamtrainingreviews.comAwesome listing on Red-Teaming trainings/platforms list of quite useful payloads for Web Application Security