The Contacts app stores all of your saved numbers or email addresses. It’s easy to add or delete contacts within the app as well though.
To add a new contact tap the ‘+‘ icon in the top left, then enter the name and the details you wish to add. Next to each option there’s usually a short description, such as home. Tap this to see other options and change to the correct type.
To remove a contact go directly to its entry and scroll to the bottom of the screen, then tap Delete Contact. Confirm that you want to remove it and it’ll be deleted.