Contacts are used to in the sharing menu to build up a address book of the persons you often share with. You can create a contact from the preferences menu.
Select the “+” and you will see this pop window where you can type in the credentials. Special the call number is important if you wants to share with “two factor authentication” where the recipient will also receive a SMS text message with a 4-digit code that is required to access the share. Just type in the country code, not with “+” or “00”
You will then be able to find you contract list in the sharing menu.