Follow these steps to install WhatsApp on your Nokia C3 :
1. Visit - http://whatsapp.com on UC Browser or Opera Mini.
2. Click on the "Download Now" button.
3. In the new page, click on the green "Download Now" button again.
4. Now, if you are using UC Browser, click on "Install" button and it will automatically install the WhatsApp on your mobile.
Alternate Method : You can directy goto this link and download Whatsapp - https://www.whatsapp.com/s40/OptWhatsApp.jad
Note : Since, Nokia C3 is an old device, it doesn't have the option to turn off data. Therefore, you need to have an unlimited data plan on your SIM. Otherwise, it will cost you money from your recharge balance.