The area around the text in a table can be increased with Padding. 

Space around the text can be increased in a different way by Spacing.  The inner lines in the table below will not be visible when viewed with a web browser.

To increase cell padding and spacing select the table, then click on Table on the menu bar, then Properties, then Table Properties.  Increase as required.

Aligning text in a cell

The vertical position of text in a cell can be aligned.  Select the cell, then click on Table on the menu bar, then Properties, then Cell Properties.  Note how Mammals is vertically aligned at the Top of the cell..

To merge cells

The heading Farm animals looks better over two columns.  To merge the two cells, select the cells, then click Table on the menu bar, then Merge Cells.

Centre the bold the heading as required.