How to tin a soldering tip:
Once the soldering iron gets hot enough to melt solder, melt solder against this sal-amoniac block. Due to the sal-amoniac bar’s chemical composition, the solder will remain on the bar. Rub the copper tip against the solder on top of the bar and a layer of solder will adhere to the copper tip. This is a useful exercise because a pre-tinned tip makes soldering easier.