Metallic bonding is the attraction between cations (positive ions) and a sea of delocalised electrons. The cations are arranged to form a lattice, with the electrons free to move between them.
The structure of the lattice varies from metal to metal, but here is a simplified form of a metallic lattice:
Properties of metals
The electrons in the metal are delocalised, so they are free to move throughout the crystal in a certain direction when a potential difference is applied. Therefore metals can conduct electricity in the solid state.
The delocalised electrons are still present in the liquid stte, so metals can conduct electricity in the liquid state too.
Melting and boiling points
The bonding in metals is relatively strong (though not as strong as in ionic compounds) so the melting and boiling points of metals are relatively high.
Smaller ions (and those with a high charge) attract the electrons more strongly and so they have higher melting points than larger ions with a low charge.
Other properties of metals
The bonding in metals is non-directional, so it doesn't really matter how the cations are oriented relative to each other. The metal cations can be moved around and there will still be delocalised electrons available to hold the cations toether. The metal cations can therefore slip over each other easily.
This makes metals soft, malleable, and ductile.