It is the basic tool for circuit making just like screwdriver for a mechanic. It is used to join two metals together by melting and flowing a filler metal into the joint (like a wire to a switch). There is an advantage of soldering that you can de-solder and re-solder easily if you have made a wrong circuit.
Things needed while soldering:
4.Stand (for safety)
5.Damp sponge (for cleaning the tip)
For robotic purposes, we will rarely need a temperature controlled soldering iron. You can buy the cheapest soldering iron available in the market but the basic question is