Electricity is the movement of electrons.
Electrons are tiny negative particles that fly around the nucleus of every atom.
Notice the single electron in the outer orbital of the copper atom. It is this single electron that makes copper a good conductor.
What we have with a copper wire is many copper atoms sitting right next to each other as in Figure 2.
As a battery pumps electrons out of the Negative Terminal into the first atom of the wire a chain reaction begins. The extra electron forces the lone electron in the outer orbital into the outer orbital of the second atom. The second atom, now has an extra electron and in tern throws its extra electron on to the third atom and so on until finally the last atom in the wire throws its extra electron back into the battery's Positive Terminal. See Figure 3.
Copper, silver, gold and platinum have atoms that are very happy to accept and pass on electrons. That why we use these elements to make wires and conductors. If a wire is made very thin then the electrons have to involve many more atoms to get them all to flow through the thin wire. This causes the wire to heat up. Now if this wire is made of an element called tungsten it can withstand very high temperatures before it melts. In fact it can glow white hot and still not melt. That is why Tungsten is used in the filaments of light bulbs.
Other metals melt very rapidly when exposed to high electron traffic. Aluminum is such a metal. I used to make fuses out of the aluminum foil wrappers from sticks of gum for science class. By very carefully cutting two notches in a thin strip of the gum wrapper it would hold up to the current drawn by a light bulb but would melt if direct battery current was passed through it.