Wireless uses radio waves to transmit information. In walkie-talkies, sound waves are converted into an electrical current, and the encoded sound data hitches a ride on a radio wave. It does this by changing either the wave's height or its frequency, which is the number of times the wave curves up-and-down per second.
Think of the unmodulated radio wave as a blank sheet of white paper, and the encoded sound wave as the ink that forms the printed words. The ink causes variations against the background of the paper, and this is what the eye sees when it "reads."
Radio uses noise instead of paper and ink. Unmodulated radio waves will have the same height or frequency. Mixing in a data stream of electrons causes slight changes in either of those two properties. These changes are detected by a receiver, which then decodes the information.
Wi-Fi uses very similar radio transmission and receiving devices to those found in walkie-talkies. They can convert the 1s and 0s of computer data into radio waves and then back into 1s and 0s. But they operate at higher frequencies, which allow for higher rates of transmission for the data.
Wi-Fi radio devices can also change frequencies. They can even split the available radio bandwidth into dozens of channels and hop rapidly between them. This makes them more immune to interference; dozens of Wi-Fi cards can talk at the same time without interfering with each other.
You can see radio wave changes as they happen on instruments called oscilloscopes. They are often used in films and television, such as Enemy of the State. When federal agents are monitoring telephone conversations from the home of their current suspect, whenever a voice speaks, the wavy green lines on the monitor change size and shape in response.