The standard method of forming electrical connections between building components and wires in electronic circuits is soldering. This type of soldering by which two metals are connected with solder is called soft soldering. Use an electrical soldering iron with a power of about 30 to 45 watts.
Solder is available at all electronics stores. It is typically 1mm in diameter and consists of a flux core surrounded by a tin-lead alloy. Rosin is often used as a flux to make the solder flow more easily. Because they contain lead, the fumes developing during soldering are toxic and should, if at all possible, not be breathed in. This can, however, never be completely avoided - after all, you have to hold your head over the soldered joint to be able to see what's going on.
The tip of the soldering iron ought to be tinned and kept clean. Clean the tip by moistening it with water and then wiping it in a sponge. Always pre-tin both parts of a soldered joint by holding the hot soldering iron against the wire and by applying solder between the tip of the iron and the wire. When the temperature is right, the solder will spread evenly. A vise might be useful in place of a "third hand" (which is frequently needed for soldering).