Here are the steps to add a contact to WhatsApp:
1. Open WhatsApp and tap the number of the person you've been chatting with.
2. Tap the three vertical menu dots at the top right-corner of your chat menu and select Add to contacts.
3. Tap Create new contact.
4. Fill in the necessary fields and tap Save to reflect the person's name on WhatsApp and add them to your address book.
I hope that helps! Let me know if you have any other questions.
