To install WhatsApp on an iPhone 4, you need to first make sure that your phone is running the latest version of iOS. This can be done by going to Settings > General > Software Update. If a new version of iOS is available, make sure to download and install it before proceeding.
Once your phone is up to date, open the App Store on your iPhone 4. You can do this by tapping the App Store icon located on the home screen. On the search bar located at the bottom of the page, type in “WhatsApp” and tap “Search”.
You should now see a page containing information about WhatsApp including its rating, reviews, price and more. Tap on “Get” or “Install” (depending on whether you already own WhatsApp or not) and wait for it to download and install onto your device.
Once installed, open WhatsApp from your home screen and you should be prompted with a set up page. Here you will be asked for your phone number which will be used as your identifier for using WhatsApp as well as to verify that you are indeed using a valid number. After submitting your number, you will receive an SMS with a verification code which must be entered into the app in order to continue with the setup process.
Finally, once you have successfully verified your number, you can start using WhatsApp! Make sure to customize it according to your preferences by going into Settings where there are plenty of options available such as notifications, privacy settings, display settings etc.
Conclusion: Installing Whatsapp onto an iPhone 4 is a relatively straightforward process involving downloading from the App Store and verifying your phone number. Once installed and set up correctly, users can start enjoying all the features offered by Whatsapp such as messaging friends, sharing photos/videos etc.