I don't have much knowledge about fitness to contribute that I haven't simply learned from other people. Here are some good links to learn about fitness:
Stronglifts 5x5 - Start here, this page has a good routine for beginners with plenty of information to supplement it.
Scooby's Workshop - A shedload of information. Some of his advice is old school, but it works. I used his Pullups For Total Beginners routine to go from being able to do 0 pullups to 8 in a row.
Jeremy Ethier - lots of good videos on recommended routines, form, and small tips to optimise your performance in small but important ways. Very scientific - references a lot of studies. I particularly like how he shows which muscles are worked by an exercise.
Jeff Nippard - similar to Jeremy Ethier. Watching his Fundamentals Series and Technique Tuesday playlists will tell you 90% of what you need to know about the exercises, but his channel is light on nutrition.
Alan Thrall - focused more on powerlifting and strongman than bodybuilding.
Art of Manliness' Get Strong Section - A combination of advice on exercise itself, and the philosophical importance of it.
BroScienceLife - completely serious advice
The Golden One - has a playlist on gym and physique knowledge which covers the basics, and plenty of training/motivation videos. The rest of his channel has political/philosophical videos about the importance of bodybuilding and other things.
The shortest summary I can give about fitness is that if you want to get bigger and stronger, you have to:
Do heavy compound lifts - bench press, squat, deadlift, row, overhead press - with correct form, exercising each muscle at least twice a week, and preferably thrice. Do isolation movements only after you've done the compound movements for that session.
Increase the amount of weight you're lifting over time. Beginners can add weight faster than intermediate or advanced lifters.
Eat enough food to be taking in as many calories as you're using, or be in a slight caloric surplus. If you're naturally skinny like me, you need to eat far more than you think is necessary.
Eat ~1g of protein per pound of bodyweight. This is achievable by eating a good serving of protein with every meal IF you eat enough calories. Again, if you're thin, you probably need to eat far more than you think.