If somebody wants to learn to draw, (in my opinion) Sycras channel is THE ressource to be checked out. He has very high quality videos and explains all the important concepts to enable you to draw cool stuff after a bit of practice.

Now, I would like to make music. Never did it before. Does somebody know a `Sycra` for Music? (so a person with an equally awesome channel, but regarding music and composing)

For example what I am interested in is making a character theme that conveys the characteristics of the person.
Lets as example say, the character is a happy knight that turns evil after some time. I want to convey that through the music theme.

Where could I go to learn such stuff?

[Ambiguity]

You could look for music theory videos, music theory is kind of the music version of the "fundamentals". However, you won't be able to apply that theory until you know what tools you're working with first, i.e. what instrument.

Search Youtube for Ben Levin and/or Adam Nealy. Both have the same analytical style as Sycra, although Levin has more beginner tutorials and Nealy has more video essays and jazz.