Click on the page that you wish to hide or display under the pages drop down from the main menu:

The Gallery Page will be used as an example:

Click on the tick that is in front of the Display Page label

The following options will be available:

Check / click on the checkbox if you wish to display the page on your website or uncheck it if you wish not to display it on your website

Click on the  button to save the changes you have made or click on the  button if you wish to cancel the changes you have made.