Hi Steve,
If you wish to add a grace note to your score, you will want to select the grace note from the 7th pane from the right in the palette. You will want to add the grace note to your measure before adding the note that it is attached to. Either that or you will want to use touch entry, by tapping the icon of the hand in the first pane of the palette. You can then tap your score exactly where you wish to enter it.