These are the learning channels which I have found most helpful over the course of learning Mandarin. Please do share your own as well!
- Mandarin Corner
This channel is well known and has a large variety of videos for all levels, including street interviews, vlogs and podcasts.
Where I think this channel really shines is in providing listening content that will help someone bring their listening skills from lower-intermediate to upper-intermediate. I credit the walk around series, where the host walks around various places talking about what she is doing and seeing, with my own breakthrough in listening.
Example video:
https://youtu.be/b_d-Yf-Gzyw
- Free to learn Chinese
This is another superb channel with lots of content focussing on HSK grammar and vocab. Where this channel really shines is that it provides teaching for all levels entirely in Mandarin. These are great for listening to in the background, and for getting into the habit of doing as much of your learning as possible in the language.
Example videos:
https://youtu.be/JBZ8UGCKq6A
- Twin cities chinese tutor
This is almost the opposite of the above channel in that the videos are almost entirely in English. This channel provides exceptionally clear and succinct explanations of Chinese grammar principles.
Example video:
https://youtu.be/jlpo7S4p5HI