Help, please? (trying to improve my English)

Are these sentences right or wrong?
If it's wrong what is the right one?

1. After dressing he watched the TV. can i not use the "the"?
2. He glanced at a radio on the other side of the room.
3. I'm good (at? on? in?) mathematics
4. (at? on? in?) television/youtube.
5. His hand is shaking from (nerves or nervousness?)
6. Too (much/many?) sounds. Why does my heart says it's many but my brain says much?
7. I started to read. What's the difference with "I started reading"

Thank you very much for your help.

edit:
which kind of sound would you think as noise?
what about when a microphone got loose and the speaker let out that screeching sound? is that noise?