At the first step of the manual input, you shell create a new journal entry (if it is not exists yet).
Press the button New at the Journal panel on the tool bar. A window titled New/Edit Journal will appear.
Fill the journal information. The fields Title and Abbreviation is required.
After adding of the Journal, select it (or select the existing journal).
Press the down arrow under the Edit button in the Paper section. Select Add new paper menu item. The New/Edit paper window will appear. Fill the information in this window, and don't forget to specify authors. To add new author, press Add button at the left down corner. If you have the file of the paper on your PC, you can import it to the library. Press Add File ... button and select the file.