Tinning the soldering iron tip.

"Tinning" a soldering iron is the process by which a thin layer of solder is applied to the to iron-plated soldering tip. The solder coating protects the iron plating on the tip from oxidation.
Most soldering iron tips are furnished tinned ready for use. The ones in our labs are already tinned.

With your solder close by and the solder sponge dampened (not saturated), turn on your soldering iron. After about two minutes, quickly swipe the tip thru a groove in the sponge. Then liberally (1-1.5in of solder) apply solder to the tip and back about 3/8 inch. Don't wait until the tip is fully hot and let it set a few minutes, because it will form tarnish on the tip. The tinning inhibits oxidation of the iron-plated tip. The tip will smoke for a few minutes while the flux burns off. Clean the burnt flux off the tip with the sponge again. Then apply a small amount of solder to the iron tip again for a protective coating and thermal bonding. Now you are ready to solder.

Warning: The tip temperature is about 400 degree C and the solder becomes completely liquid at 361 degree Centigrade. Splattered solder will stick to some clothing and will melt thru polyester or nylon clothing (like $400 gortex jackets) and of course will burn you slightly.