"bump"sticks (cams) open and close intake and exhaust valves at the appropriate time in the engines 4 stroke cycle.
The cam is tied to the crank via the timing chain, right.
At certain points in a pistons stroke it will generate a greater force of pull and push (to take in air/fuel and to evacuate the spent gases once the mixture is cooked by spark).
The idea behind advancing/retarding the timing is to set the optimum time that you want the valves to open and close based on the specifications of the cam.
You advance/retard the timing by rotating the cam a few degrees clockwise/counterclockwise while the crank remains in the same location in its revolution, then install the chain to keep them tied at this relationship to eachother.
The majority of street cars are set at zero ... neither advanced nor retarded.
This is "Advancing/retarding cam timing", because it affects the relationship of the valves and the pistons. A lot of guys will say, "I advanced cam timing 4* " to refer to this procedure.
"Advancing the spark timing" deals with turning the distributor cw/ccw to adjust the time at which the spark is sent to the plugs to detonate the a/f mixture. This relationship involves the timing in which the fuel is ignited and where the piston is in its travel. A lot of times you'll hear guys, "I have my timing advanced to 12* " This is what these guys are referring to.
The old belief was that advancing the cam would give more low-mid power and retarding would yield a little more top end..
Based on current dyno testing, this is not the case.
Typically advancing a couple degrees will give an engine a few more hp/tq ... and retarding will yield zero to negative results.
This procedure is usually done by competition guys to squeek out each bit of power they can, and not too common with the daily driver/street crowd.
The gains aren't rewarding enough for most to do the procedure ... however if doing an engine build and swap moving it a couple degrees advanced doesn't hurt (with most grind cams) ... You should always be aware of your valve and piston clearances.