Each atom has a nucleus, surrounded by electrons. In a solid metal all nuclei are bound to their equilibrium positions. But some electrons are free to move throughout the solid. They can easily pick up kinetic energy in collisions with hot cores and loose it again in collision with cooler cores. Since their mean free path between collisions is larger than the distance between neighboring atoms, thermal energy can move quickly through the material.
Metals are, in general, much better conductors of heat than insulators.
Convection Convection transfers heat via the motion of a fluid which contains thermal energy. When a fluid, such as air or water, is in contact with a hotter object, it picks up thermal energy by conduction. Its density decreases. For a given volume of the fluid, the upward buoyant force equals the weight of this volume of cool fluid. The downward force is the weight of this volume of hot fluid.