How is digital data represented in analog waves?
If you want to know how 'A' from from keyboard via Bluetooth to your computer starting from 1s and 0s on an analogue wave, then it's far too complicated for any person to think about all at once.
So we divide it into layers. Each layer uses the services of the layer below, and provides services for the layer above. This allows us to concentrate on just a few simple problems at a time.
The lowest layer is called the physical layer. This handles the radio signal. Start with wikipedia, and look up, in this order, simplest to more complex, Amplitude-shift_keying, Frequency-shift_keying, Quadrature_amplitude_modulation. We rarely use ASK, it's too inefficient. There are more modulation types, more efficient and much more complicated than QAM, but those three will do to get your started.
The highest layers are the applications in the keyboard and computer. The keyboard app asks the layer below to 'send 'A' to a machine with this identity', which happens to be your computer. That layer then calls a lower layer, which resolves the identity to an address, formats the message, and eventually the data trickles down to the physical layer and becomes variations on an RF carrier.
There's a whole bunch of layers in between that handle the connection, know about identities, get messages resent if parts are missing or garbled, and a whole lot more. Have a look at OSI Model or the TCP/IP stack if you want an idea of all the stuff that can happen in between, but don't expect to understand it or the need for it at a first reading.