Assuming you have a camera, either built into a laptop, built into a monitor, or just a USB plug-in webcam, you still have to go to the Win 10 Camera Privacy screen and make sure the camera is turned on.

Then scroll down that same screen and give permission to each Microsoft app and each desktop app you want to use the camera...

And you'll also need to do the same on the Microphone Privacy screen, if you intend to use a microphone, regardless of being internal (laptop) or an external plug-in

You should identify your model computer. Windows Hello requires a high end camera that is on more expensive laptop models. See this for models that qualify--

https://support.microsoft.com/en-us/help/4028017/windows-learn-about-windows-hello-and-set-it-up

Desktops do not have cameras.

Not surprisingly that link gives no information about the models that qualify. Surely it should be a Dell link, which would be very helpful.

What is your model computer? All Dell computers have that screen about Hello, but just a few laptop models actually support it.   

Every Windows Hello Compatible Laptop | Windows Central