Moving the horizontal and vertical lines modifies the size of the table cells. Move your mouse over a line until the cursor turns into a double arrow. Now pick up the line and move it to the desired position.
To create a field containing text information click on the icon "Text" and open a frame in the desired cell, in table, header or footer. You will see a text frame containing the word "empty" appear in the cell:

The handling of these text frames is identical with the text frames outside a table. Double click the frame to enter the text directly into the editor or drag and drop an XML node into the right frame to make a connection
For your convenience, it is also possible to directly drag XML nodes into a table from the XML tree. Select a node from the XML data source on the left side, click on it with the mouse, keep the mouse button pressed and drag the node into the table cell where you want it to be. Release the mouse button. You will see that an XML frame has been placed in the cell, but now it already shows the node name including the correct path up or down the XML structure, depending on where you grouped the table to.

Please note: XML elements display their content in curly brackets, whereas static text does not display any automatic brackets. The curly brackets inside text elements are usually used to indicate XML nodes or functional elements. It is nevertheless possible to write static text in curly brackets, these text parts will then be displayed in a box with a blue dotted line around it in the text editor window:

This effect does not influence the display in the output, however.
If you would like to add XSL code to control table cells, use the icon "XSL code".