parse serial packet

This is something Ive been having issues with and wondered if someone could help. I simply want to control the pwm duty cycle on pin 9 and 10 from Pure data. One idea I had is i will send 3 bytes to the arduino

pwm1, pwm2, end_signifier

Ill use 255 for end signifier (dont mind loosing one value for the pwm).

What would the set up of and serial.available look like for this. If anyone could point me I'd be super grateful. Do i need to set up some kind of buffer?