Lichess is a superb website which combines online tournaments, game studies and tactics. It is all open source too. A great example of people coming together to create something great.
Is there any way to know which videos are good for which levels on the St. Louis Chess Club channel?
They have playlists for different levels of player:
1. Kids' Beginner - https://www.youtube.com/watch?v=q7kkP5en4Qo&list=PLVWaFpMwta...
2. Beginner - https://www.youtube.com/watch?v=n8XxkotWVkY&list=PLVWaFpMwta...
3. Intermediate - https://www.youtube.com/watch?v=Ym8KgIfeMtE&list=PLVWaFpMwta...
4. Advanced - https://www.youtube.com/watch?v=k_g5Wyb57xQ&list=PLVWaFpMwta...
The St. Louis Chess Club has a great collection of Chess lectures at various levels: https://www.youtube.com/user/STLChessClub
I also like Agadmator's YouTube channel - he analyzes famous games as well as games from current tournaments and such: https://www.youtube.com/user/AGADMATOR
I also like chesstempo for puzzles: https://chesstempo.com/
I'm not very strong, though, so take what I say with a grain of salt.