To add a row or column to a spreadsheet, right-click on the gray area containing the column letter or the row number. Select the action that you'd like to complete. For example, to insert a blank column to the left of the column you selected, you'd select Insert 1 left from the drop-down menu. To delete a row or column, select Delete row or Delete column from the drop-down menu.
If you'd like to insert multiple rows or columns, highlight the number of columns or rows you wish to insert. Then, right click the column or row header, and select "Insert N..." For example, if you highlight five rows, right click the row header, and select Insert 5 above or Insert 5 below.
To add a large number of rows (100+) to your spreadsheet all at once, scroll to the bottom of the spreadsheet. In the text box, enter the number of rows you'd like to add and click the Add button.