Select the table icon.
Set the rows and columns. For now, these cannot be changed after the fact without adding HTML code.
Here you can also set border, spacing (distance between cells), padding (distance between content and the cell border).
To add a row, look for the last <tr> </tr> before the </table>. Add another <tr><td></td><td></td></tr>. <tr> is a table row. <<td> is a table cell. You're best copying the last <tr>...</tr> with everything in between and paste it between the </tr> and the </table>. Columns are made by how many <td> are in the row. Make sure there is the same number in every row.