Non Coherent Detection of Digital Signal
Assuming you have a modulator, a usable wireless channel, a receiver and a demodulator, an example of a simple communication synchronization technique is to use what is known as a preamble. The preamble is sent prior to sending real data (pay load). In between preamble and payload is a header. So, you transmit: -


Preamble (a series of bytes that are recognizable from payload data or the  header)
A header - marks the end of the preamble and tells the receiver that the preamble has finished and that the next byte is data. It may also tell the receiver how many bytes are contained in the pay-load.
Data (might be fixed length or variable length)
Checksum - this allows the receiver to compare (or measure) that what was transmitted is the same as what was received.


Because the preamble is "special" it can be recognized from pay-load data and hence, when the receiver sees it, the sync process begins. Because the preamble is a repeated "special" bit pattern, it doesn't matter if the receiver misses the first one or two repeated patterns.

If the receiver doesn't see preamble then it waits until it does. This means that real pay-load data can be missed but that is the price you have to pay for usable and reliable data communications. Here's an example using FM modulation: -



See also this EE page for a slightly more comprehensive answer.