The following series of photographs show the process of tinning wire (coating the exposed wire with solder). Care should be taken not to overheat the wire but it needs to reach a suitable temperature for the solder to 'take' to the bare wire.
Before commencing, make sure the soldering iron has had sufficient time to heat up. If the tip is dirty, wipe the tip of the iron on a moist sponge (a kitchen sponge will do).
A small amount of solder is applied to the iron to facilitate heat exchange between the iron and the wire.
The iron is placed in contact with the wire.
About half a centimeter of solder is applied to the junction of the iron and wire
The solder melts. Note the whisp of smoke caused by the resin core of the solder
(perfectly normal - the resin core is a flux)
The solder is removed.
The iron is slid alond the wire as it is removed.
An instant after the iron has been removed.
The wire is now tinned.