Some composers compose with their pencil and paper, some compose with a guitar or a piano, and some compose with a french horn in hand. There's no right way to start writing sheet music, but it's helpful to be able to play yourself to practice out little phrases you're working on and hear how they sound.
- Plunking out some notes on the piano is especially useful for composers to know, since the piano is the most visual instrument all the notes are right there, laid out before you.