It's not a stupid question. Timing has to do with the exact moment the spark ignites the air/fuel mixture. Consider how a four cycle gasoline engine works. It takes time for the combustion process to take place. Why does it matter?
If you fire the spark too soon, the piston is still moving up in the cylinder. Fire too late and the piston is already moving down the cylinder. Remember that the combustion takes time. So at idle you may want to fire the spark about 10 degrees of crankshaft rotation before the piston reaches the top of it's travel. (TDC - top dead center) That gives the air/fuel mixture time to burn(explode) and push the piston down the cylinder.
Simple enuf. But consider this - the combustion takes the same time but if you want to go faster, the engine has to turn faster. So as the engine speed increases(RPM's on the tachometer) the ignition system has to fire the spark sooner to give good power and economy.
How do you measure timing? You use a timing light. It's like a strobe that fires with the spark of number one cylinder. You aim the light at reference (degree) marks on the crankshaft pulley and a pointer and make adjustments if needed.

dave and xtoy - out of *time*