The step by step procedure of adding new contacts numbers in your whatsapp is following wether you are using on android phone or i phone or samsung etc , wether the contact is from usa or india the process is same.
1- open whatsapp in your mobile phone
2- go to contact tab and click on add contacts on top .
3- enter the name of person whose number you are adding
4- save it & refresh the contact from top .
5- if you are adding him for first time and he is not in your contact list then send him a message .
6- once you send he will belisted in your contact as wellas your chat