Say you want to create a social network for soccer moms to chat and commune. Instead of building up the social site first and relying on the 8 soccer moms you know to get it going, it's better to create a blog with tips targeted toward soccer moms. Build it up with stories and useful tips other soccer moms need.
The main composition of a soldering iron is a metal tip, which is heated in an insulated handle by either gas combustion or electricity. Today, electronics soldering iron is widely used in repair jobs, installations, electronic assemblies and so on. It is also used for pyrography as well as plastic welding, although very rarely seen.
Solder is basically metal wire with a low melting point, where low for our purposes means low enough to be melted with a soldering iron. For electronics, it is traditionally a mix of tin and lead. Tin has a lower melting point than Lead, so more Tin means a lower melting point. Most common lead-based solder you'll find at the gadget store will be 60Sn/40Pb (for 60% tin, 40% lead).