Since WhatsApp uses people’s phone numbers as the foundation for all profiles, you can’t “find” someone on WhatsApp if you don’t have their phone number. If you have them in your contacts but you aren’t sure they have a WhatsApp account, you can tap the “Chats” button on the bottom of the screen, then click the “Compose” button to send a message, and start typing their name. If they have the app, their name will show up.
When it comes to adding people, you can do it two ways: you can either add a contact in WhatsApp or use your default Contacts app. When you add a contact to your phone’s address book, it will load in your WhatsApp contacts immediately if the person has a WhatsApp profile.
To add a contact through WhatsApp, you can click on the chat icon at the bottom of the screen and then select the “Add new contact” option at the top.