solder tips(help) recommendations
Modern electronic soldering iron tips are plated with iron, overtop of a nickel barrier. The tip itself is made from copper. 

If you abrade it with a file, grinder or emery paper etc. you will damage the tip plating and the exposed copper will quickly dissolve into the solder. 

To clean the tip of flux and excess solder, a damp (not sopping wet) sponge works great. 

Your wire is probably tinned (which means it has a solder coating, which may be mostly tin or tin-lead solder) copper. If you cut it off and look at the end under a magnifier you can probably see the copper color. 

Of course wire can be made from any material- aluminum, gold, nickel, nichrome, silver, stainless steel, iron etc. but many of those materials are either expensive or difficult to solder with relatively benign fluxes. 

Different jobs call for different styles of tip- here are a few that are compatible with Hakko soldering irons: