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.
runner work is not too hard if your just gasket matching and cleaning them up a bit its gonna be hard to mess them up just dont take out too much material and keep an eye out for the water jackets. You should practice on a dead head that i'm sure you'll have lying around at your job to get a feel for the grinder Bowl work leave to the pro's that's where things get complicated.