Conductors transmit very well the electronic energy
Metals are usually the best electrical conductors: their atoms arrangement is very well structured and narrowed, so that when applying an electrical field onto a metal (e.g. using a battery), electrons are attracted into one direction and trarvel very quickly from one atom to its neighbours.
Insulators transmit very weakly the electronic energy
Conventionnal paper, as well as most ceramics or plastics have a highly disordered internal structure, and electrons can hardly travel inside these materials with regular power sources. "They do not conduct the electricity".
And in between?
Other solid materials can be in between conductors and insulators and are said to be semi-conducting materials. The most famous of these materials is silicium, which is at the basis of electronics and computer science as it enables to produce transistors.
How to use them ?
All those materials are useful in electronics. For instance, an electrical wire is made of a highly conductive central wire covered with a plastic insulator, so that electrons are contained and must follow the circuit.
Is that all I need to know?
Nope! Combining various materials together enable to produce new types of solid materials such a semi-conductng papers. These new materials can enable the production of other electro-active componenent such as sensors and transducers. .
Liquids such as water or acidic solutions used in batteries can also be more or less conductive, but this is another story!