Don't know this specific boiler but in general there will be a spark generator button which is pressed repeatedly until pilot is lit whilst pressing and holding in the gas control (rotary knob which has three positions ,, ON, OFF and IGNITION, you need to select ignition position of course and hold it in for approx 15 seconds after pilot is lit and then release and turn it to ON position).
So, it's gas control knob to IGN position, press and hold it in then repeatedly press spark generator button until pilot lights. Continue to hold in gas contol knob approx 15 seconds so that when released pilot remains on. If it goes out repeat process. Then turn rotary gas contol to ON position.
I presume you have looked for instructions which are normally printed inside contol cover ?
Keith, July 2006