According to the structure of metals, how do they conduct electricity? I can't explain it if you can help me please.. The structure is about positive and negative..

If you take 1 metal atom, you have a nucleus (which is positively charged: all the protons are in it, as well as the neutrons) and a bunch of electrons circling around the nucleus. The amount of electrons is the same as the amount of protons.

 

In a metal, the atoms are arranged in an orderly structure. The thing that distinguishes metals from other materials is that the outer orbitals overlap (the electrons that circle the furthest from the nucleus have overlapping orbits) . This means that an electron in this orbital can do half a circle around one nucleus, then continue around the next, and the next, and the next etc. And it can go through all the length of a wire... which means it is conducting.

This is often referred to as an electron sea.

Put it this way. Electricity is the flow of electrons between two points. In a metal, the outer electrons aren't really "bound" to one lone nucleus. As frosch45 pointed out, it is a "sea of electrons". When an electric current is applied to a metal, the electrons that are applied are able to "push" the electrons in that sea forming temporary charges on certain parts of the metal. This "pushes" the electrons in the metal around and ultimately through to the other side, hence the conduction.

 

Now keep in mind that my explanation is very rudimentary and the actual science of it is more complex, but a good visual analogy is to take a carboard box and fill it completely with clay. Now have a hole on opposite ends of the box. If you go and push more clay into one side, clay will extrude out the other side. In this example, clay are the electrons and as you add more, some of it will come out the hole on the other side.