A screen reader cannot read information in a table when it has nested tables, split cells, or merged cells. Generally, tables are best used for numerical data. Tables must have a header row (formatted top row), and often but not always require a header column (formatted first column on left).
Why? A screen reader audibly reads the data from left to right. The top row (header) has to be formatted so the screen reader knows to read the information in that row first before reading the information below it.
If the header is formatted properly, the screen reader will read each row by first reading the title found in the header, at the top of the column, so you can tell what type of data is being described.
If you are creating a table on the website, click "header row" and if needed click "header column".