There are various ways of joining metal, depending on the function and quality of the product, and the strength required.
Soldering is a technique used in plumbing and electronic industries to join metals by melting a filler metal (solder) into the joint. Brazing is also a type of soldering using a filler metal with a higher melting point.
If you are working on electronics and computer equipment, soldering wires will form a better electrical connection than using wire nuts and electrical tape.
Welding is different from soldering in that the base metals being joined are themselves melted, fusing together as they cool. In oxy-acetylene welding a very hot flame is used. In electric arc welding a spark heats the metal.
Rivets are fixings with cylindrical shafts and a head on one end inserted into pre-drilled (sometimes countersunk) holes to join metals. The end of the rivet is beaten into a dome to keep it in place and the joint is finished using a rivet set or snap.
This technique is used to join thin sheets of metal, such as aluminium, when you only have access to one side of the joint. Pop rivets (otherwise known as blind rivets) come in different lengths and diameters, so choose the right type for the combined thickness of the metals you are joining.