This is not a perfect explanation, but I hope it helps.
When something is frequency modulated there are 2 frequencies, I would not define one as "normal".
There is a frequency that is a digital 1, there is a frequency that is a digital 0.
So, when you are receiving, lets look at a conceptually simple detector. You have a bandpass for each frequency, and on the output of these, you have a rectifier which measures your relative power.
When you are receiving, you need to know the bitrate, or you need a shared clock (which requires a second connection to clock the data, or a second communication channel that cycles between its two frequencies to send the data). Often you read off of the two rectified signals as if you were reading a UART line.
Normally your data rate is significantly slower than your modulation frequency. Normally by a factor of infinity, which in engineering we can get by as approximating as 10.
Please let me know if there is something I can expand on to make this make more sense.