Serial data is just 1 and 0's.

So if receving say a byte the the serial packet will have a start bit, 8 bits of data, parity bit and then Stop bits.

But it is all done on timing, so if the pic does not receive a say a 1 within the time delay set by the baud rate between bits, then it will just take it as being a 0

This is where you need to use the parity bit and do a calculation against the 8 data bits received.
So basically receive your 8 bits and your parity bit, do the calculation and if incorrect request the byte again from the device sending the data.

Regards

Sean.