Just to be clear, wifi uses radio.
All those signals are photons that fly around and behave both like particles and like waves. As particles, they bounce around and have a linear component to them, but as a wave they have a frequency in which, once emitted, they oscillate in as they travel.
There is a spectrum of those frequencies that we call the electromagnetic spectrum. And every frequency range in that spectrum has different properties. Visual light exist on that spectrum. What happens is that we as a species developed organelles (cones and rods) in our eyes that interact — pick up that spectrum. But that is a very narrow band in that spectrum.
Radio signals are much higher wavelength and lower frequency, and that range has several properties — good propagation through the air, little in the way of signal deterioration and interacts with wires and antennas. This means that you can emit signals in those frequencies they can be picked up somewhere else in the speed of light. It started with simple signals that created tones for someone to hear and interpret by a user, but it slowly became progressively more complex so that only electronic systems can process them, but the principal is the same.
EDIT: A correction as detailed below.
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