Pages for the mac: Table Modification

Greetings all. I have looked all over this site, but have not yet found the answer to the following question. I just got pages for the mac, and I am trying to work with tables. I can insert one just fine, but it gives me a predefined set of columns and rows. How do I change this? I want to add and delete rows/columns. I have figured out how to delete columns and rows, but is there a way to delete several columns and rows at once? Also, how does one add columns and rows? Thank you very much.