Electricity is a form of pure energy. The electricity that you are using now to power your computer so that you can read this has been made a few milliseconds ago in a power station or a wind turbine. It is the job of the national grid to balance the amount of power that is being consumed with the amount being generated. Sometimes a fault in a power station causes it to shut down suddenly, if this happens then there is less electricity being generated and the electricity being delivered to each user losses some of its power, until the generation can be replaced. This manifests in a lower grid frequency and voltage level, and sometimes this causes a short term spike in the wholesale market price.
Voltage is defined as electrical potential difference or electric tension, but it is much easier to think of voltage as being equivalent to water pressure. Imagine a water tower in your town with a hose pipe connected to a tap at the bottom. The higher the water tower means the higher the water pressure.
Current is a bit easier to understand as it is simply the number of electrons flowing in a wire at any time. Going back to the water analogy, current is the volume of water flowing down the hose.
In its simplest form power is voltage multiplied by current. if we revisit the water tower again and open the tap. The volume of water multiplied by the pressure of the water gives the power. We can increase the power by making the hose bigger so that more water flows down it, OR by making the tower higher.
Electrical resistance slows the current flowing in a cable. A smaller hose has more resistance so less water can flow. effectively this reduces the power available.