Gapping a spark plug is important to get the best performance from your 'ped. Gapping is ultra easy to do and takes 30 seconds.
You'll need a spark plug gapping tool, available at any auto parts store for $5. It looks like a deck of skinny metal cards all riveted together in one corner. Each metal card is thin and a specific thickness, which will be written on the card.
Read your owner's manual and find out what spark plug gap you need for your 'ped. Let's say for example that the manual says your gap should be 0.6 - 0.7 mm (0.024 - 0.028"). Open up your gapping tool and go find a metal card that is between these numbers, say a 0.610mm card. Grab your spark plug by the white ceramic end, spark plug threads and electrode side pointing up. Shove the 0.610mm metal card in the gap between the curved metal and flat metal parts. This is where the spark from "spark plug" happens.
If it can't fit then use pliers and carefully make the gap a little bigger. Try other metal cards such as 0.635 and 0.66mm. They should all fit. Then try a 0.711mm, which is too large for your optimum gap. If this metal card fits then your gap is too wide. Use pliers and carefully make the gap smaller, or push it against something to bend it so it's smaller. Recheck with your metal cards. When your gap is within your manual's specifications you're done.