If you are bonding wires to the PCB, strip away about 8mm of the plastic insulation to reveal the conductor. In the case of “Stranded” wires, twisting the conductors together will allow them to go through the PCB easier.
Since you will mostly be working “upside down” there is a tendency for any components or wires your are soldering to want to drop back out the hole you have put them in. Adding a slight bend to the legs or to the wire once you have them through the hole will prevent this. Alternatively you could hold the parts in place with some tap
Heat the wire or component leg at the point at which you wish to create a joint with the iron. Once the metal is heating, touch the tip of the solder wire between the iron and the wire / component so that it melts and flows into the hole and on your wire, joining them together.
Once enough solder has coated the join (it should only take a few seconds), carefully remove the iron and allow the solder to cool.