In accessible forms, screen readers speak information about where the cursor is located in the table. As a user moves between the table cells in a form, the screen reader speaks the contents of the cell. When a user moves to a cell containing a nested table, the screen reader speaks the contents of the cell and the nested table.
The editable fields in a nested table are part of the tabbing order in the form. Therefore, users move between editable fields in a nested table by using the arrow keys. As the user moves in and out of a nested table, the beginning and end of the table is spoken.
See also 

About navigating tables in accessible forms