Yes, you can have as many pages as you need that are not included in your navigation.
Once a page is added it immediately has a live URL. So if you add a page called “Mission Statement” it will automatically live at www.domain.com/mission-statement until you edit the URL address. If you do not want to add that page into your navigation, you can link to it from either an image or text on a page using the link tool in the content editor.
If your intent is to have semi-private content that is fully accessible but not immediately visible to a visitor, you may want to create a page with a list of links to the pages that are not in your navigation. Some people have found this helpful for their worship teams, children’s ministry, small groups, etc. TO do this, first create the page and then add a bulleted list in your content. Select each individual item in the bulleted list and use the link tool to link it to a page, event or file.