The heads are ported and polished meaning the intake and exhaust runners are gasket matched and or modified (ported) and then the casting flash and ridge from casting the heads are smoothed down (polished). The valve seat's can be removed to accommodate larger valve's the valves can be shaved slightly different sides of the valve's allowing for better flow around them (angled valve job). For the cam the lobes are ground differently to increase valve lift (how much the valve opens) and duration (how long it's open for). Intakes are just gasket matched and or modified and polished for better flow. Thats pretty much it hope i explained it well enough for you.