Users of screen readers cannot interpret tables the same way sighted users do. Sighted users can tell at a glance what column and row a given cell is associated with, but a screen reader user needs a properly coded table. To make tables usable, additional steps will need to be taken to make them accessible.
The image above displays a simple table: books read by two people. Only column headers are needed to identify who read which books.
In the image above, there is a complex table: books read by two people each week. Both column and row headers are needed.
In the second example, a screen reader user will know that The Sound and the Fury was the book read by Tomiko on Week 3.
When adding tables, add a row and/or column to be used as a heading for each as appropriate. The table creation menu contains a Headers option that allows for designating the first row, column, or both as headers.
Add a Caption, if necessary, to the table to inform readers of the table's content. Good examples are "Data from recent study," "Table of inputs and outputs," etc.
Tables should only be used for tabular data, not for layout.