When you click on the "check in sheet", do you see the student's name on the left? If so, you should be a column highlighted in green where you can put in your code.
To go back to your notes, click on the Class spot and the student's name. Your latest conference should appear at the top. If you want to add something, click on the "edit" tab, and you can change/fix, etc and save there.
I hope these are clear, but if you have any problems, please don't hesitate to ask.