A soldering iron may be one of the simpler pieces of electronic repair equipment you will use, but it needs regular maintenance in order to operate properly. If you do not keep your soldering tip cleaned and properly maintained, then it will not be able to heat up the solder enough to get the job done.
The SITC01 is a replacement solder tip cleaning wire sponge. These sponges are hard enough to remove debris and some corrosion from the solder tips while being soft enough not to damage the tip. They help to remove oxides and excess solder to preserve tip life and enable clean, precise soldering.