Navigate to your experiment, and then to the appropriate subject (in the tree view under "Subjects and files"), and then to the appropriate session (in the tree view under "Sessions and files"). Click on the session. The session view is shown, including a blue button labelled "ADD NEW MODALITY". Click this button.
Fill in the form (all fields). Click the "Files" tab to add folder or files from your PC. Click the black button: "ADD FOLDER" or ADD FILES" and select files from your PC.
Finally, click the blue button: "SAVE". A view of the new modality is displayed, with a green notification message saying: "Complex modality was successfully created."