To add a row to the end of a table, click the mouse anywhere in the bottom right hand cell and press the Tab key.

To add a single row in the middle of the table, click in the row next to which you want it to go, right-click the mouse, press Insert, and choose whether to insert Above or Below.

To add several rows to the middle of the table, select the desired number of rows next to which you want the new rows to go, right-click the mouse, and press  Insert (choose whether Above or Below). The number of rows you selected will be added.