Cylinder Heads
Cylinder heads are made of either aluminum or cast iron. Today's vehicle will typically have an aluminum head for a lot of good reasons. Aluminum heads are lighter sometimes as much as 50 lbs. 
They transfer heat to the coolant better than their iron counterpart.
The cylinder head contains the engine valves, valves springs, and valve seats. The valve train can be very different depending on the type of cylinder head you are working with. The location of the cam has everything to do with the type of valve train used on the engine.
An OHC (overhead camshaft) engine would have a rocker arm assembly or the camshaft would ride on a tappet bucket. 
An in block type camshaft would use lifters, push rods, and individual rocker arms to open and close the valves.
It's vital to remove the heads from a cool engine. The head may warp if removed hot. Even if the engine is just warm I'd wait. Also get the torque specifications and remove the bolts in the reverse order of installation.
After removing a cylinder head from an engine it must be cleaned from sludge and carbon deposits. This is important as a thorough inspection should be done. Use a brush and mild cleaning solution in a parts washer or a canned product like GUNK™ engine cleaner.
Inspect the cylinder head for cracks that typically form between cylinders and around coolant jackets. Look at the head gasket for signs of coolant or compression leakage. Excessive carbon buildup could be caused by leaking valve seals or piston rings.
After the initial inspection the cylinder head the valves are removed. After this it should be thoroughly cleaned from all carbon deposits and inspected for cracks and warpage.