How does an antenna differentiate between different signal waves?
The antenna can't tell the difference between signals at all.
Even if an antenna is broadly tuned to a band, there could be many different transmissions within that band. It is only with tuning, filtering, mixing and finally decoding that the signals you are interested in can be differentiated from the rest.

For example, to receive simple AM broadcasts you could have a non-tuned antenna and feed the signals (all mixed up) into an RF amplifier and then into a mixer fed also by a carrier frequency of your choice (a local oscillator). When you mix the carrier signal with the modulated signals from the antenna you get product and difference signals. The difference signal turns out to be the audio you desire. You could start reading here.