WhatsApp for Beginners
Step 5 Invite friends you did like to message to use WhatsApp
Tap on the Contacts tab in the middle of the navigation bar. Find a contact and tap on it to view its details. Tap Invite to get WhatsApp to send them an SMS invitation to download the app.
If you use this option to invite a contact from another country, both of you may be subject to international SMS charges. You may want to send them an email to join WhatsApp instead. To do this, go to Settings >> Tell a Friend and then select the method of delivery.
In order to message a friend on WhatsApp, they must have been added into your phones contacts. Ensure that their phone number has been entered into your address book accurately and that they have installed WhatsApp.