You can edit the cells in a schedule by clicking in them. You can either select a value from a list (if available) or enter text. As you add new values, they become available in that field's list.
To enter carriage returns in a text cell, press Shift+Enter. Carriage returns display when you place the schedule on a sheet.
For schedules grouped by type, changes to a type are propagated to all instances of that type within the project.