My smartphone doesn't have built in wifi so i was just wondering if there is any app to add wifi to my device???

Not having WiFi means your device is missing hardware & if that's the case & its not just your Wifi is not working, you can run a USB cable to your PC & use its Wifi but you'ed now be tethered to your PC. Or depending on your device plug in a "Wi-Fi USB Adapter" & see if your device can read it & if so you'd be 100% portable.