Click through these 4 steps before you start the data entry exercise:
View the scanned page on the right of the screen and the data entry fields on the left side of the screen.
Enter the whole text in the transcription field.
When you find a date, location, event, name, unit or valuable keyword, choose a field to enter the data separately.
For every new field you choose, a new data entry field will appear.
When the whole page is transcribed, you can press "finalize" to save your work.