You can draw accents or marcatos on individual notes, but sometimes you'll want to apply them to many notes at once. In these cases, it can be easier to use the Accents brush.
This brush is directional, like many of the symbol brushes in StaffPad. You can just paint over notes to apply an accent to them, and drag the Pencil up to change them from accents into marcatos.
To remove them from notes, paint over the existing notes and drag the Pencil/pen down.