In the Dossier overview screen, on the top right, click on the "Create dossier" button.
You will get 2 choices, click "Create new".
Fill out all required fields (noted by a green * ).
Ignore the Paste button for now. This feature is used for inserting data into fields faster, but requires data in the correct format and won't fill all the required fields.
After filling out all the fields and clicking the "Create dossier" button. You can start adding more data to the Dossier.