Hi Helen-
There are two ways to make sure your page shows up in your menu.
First, when you’re actually editing the page, look for the In menu: option inside the Publish box.
The other way is inside your Customize > Menus area. Select the menu you’re working with, click Add Items and expand the Pages section. Here you’ll see all of your published pages to add to your menu.
Keep in mind that if your page is still a Draft, you won’t be able to add it to the menu until you’ve published that page.