The stepper motor kit comes with some ribbon cable wires.
You will need 2 x 2 wires and 2 x 4 wires.
They should be soldered onto Pi thus.
You may want to solder on a normal female header and plug the wires in, rather then permanently soldering but that does reduce headroom slightly. There are other configurations (to follow) where this doesnt matter.
You will need to identify the positive cables on the 2 x 2 cables, so choose a colour you will remember.
There are many good videos on soldering, I would just say 2 things.
– Use flux.
– The soldering iron doesnt touch the solder. Soldering iron heats up parts till solder flows.
(Pi graphics provided by tomnappey , ruined by me).