The default setting is that new rows are added to the end of the tables. To move the field pointer to the last row of a table, press Ctrl + Down arrow. In the preferences for the window you are using, you can specify that you want the field pointer to be in the last row when you open the window.
When you have finished entering data in a row and the cursor is in the last field in a row, you can add a new row by pressing Enter.
If you want to enter data in a number of new rows, it is a good idea to adapt the window for data entry, for example by putting the most frequently used fields first and hiding fields you do not need.
Remember that a new row may change position after you save or refresh the screen, depending on the fields the window is sorted by.