You are free to choose any form of notation i.e. Handwritten, Sibelius, Musescore, Soundtrap, Garageband.

2a. Choose an instrument/s that you would like to record your ostinato

2b. Pick a time signature for your ostinato

2c. Notate your ostinato. (If the rhythm dictation to traditional notation is difficult you can record it on Soundtrap and then export to Flat.io or Noteflight then copy onto Sibelius or Musescore)

2d. At this point you can change your C scale to a different note scale using the 'How to build scales' sheet.

Ostinato Example (Skipping rhythm using notes from the C major scale)

Ostinato Example (Skipping rhythm using notes from the E major scale)