Pages should only be deleted if they are not going to be used again. Pages can be hidden and reinstated using the Hide option instead. Hide is a better option than delete if the page might be reused at a later stage.
Pages with sub-pages may not be deleted.
In Page Properties there is a button with a Waste Basket and warning icon. If you are editing the Page Properties this button will delete the page.
If you intend to use the page again in the future use the Hide option in the page header instead of deleting.