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 right, 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 tap Edit in the top right corner. Now scroll to the bottom of the screen and tap Delete Contact. Confirm that you want to remove it and it’ll be deleted.