Electrons are.. we don't really know what they are. What we do know is that they have a "charge" around them, an "electric potential", and that they repel each other.

"Electricity" is one of those terms that doesn't really have a specific meaning. From what i see, we use it to group all the electromagnetic things that.. i guess deal with "loose" electrons.

As for the actual question, first i'd have to explain "electric current". Current (in Amperes) is just the flow of electrons. As in how many electrons flow through some plane over time. In practical terms; how many electrons flow through a wire, where the "plane" is the diameter of wire.

Voltage is a force. Imagine that the electrons weren't points that repealed each other, but were instead balls. You fill up a pipe with balls and push on one side of it. The force you are pushing with is the "voltage". You can also imagine this with water, where the pressure is.. well it's all the same really when we get "low" enough. Note that electrons, unlike balls and water, don't really have mass.

Wattage is power. It is how much energy is.. transmitted over time. You pay your bills in Watt * Hours, but you might as well pay it in Joules. It shows you how much power you can expect from a machine. Wattage is calculated by multiplying Voltage and current, as in how hard you push and how many electrons you push per time. In water terms, it is the speed of the water multiplied by how big the river is (or pipe).

So they are useful units of measurement, just as any other metric unit of measurement. In fact Ampere is one of the seven basic units of measurement in the Systeme international d'unites (SI, often called "metric").

The one that actually hurts you is the current. The thing is that Voltage "pushes" the current, so one might rightfully think that "high" Voltage is the dangerus one. But again you can touch a 100000 Volt sphere on top of a Van de Graaff generator, because it doesn't have enough electrons in it to make a current "big" enough to kill you. The current across the heart, that is enough to stop your heart, is about 50mA (as far as i remember), and that is very little current. Your heart is in between your hands, so you would need to hold "+" in one hand and "-" in another for current to go through it. You can also die from poisoning if a large current burns your flesh, and other similar bad things. If you think there's a danger from electricity, use just one hand so that the current goes through your legs, missing the heart (also watch for the top of your head, because brain). If the voltage is really high, like a transmission line cable falls right beside you, put your feet together and hop away. Like 10 meters away should be fine, idk. To be clear, you can touch the leads on your 12 Volt car battery and nothing will happen to you, in spite of the car battery being easily capable of delivering a big(ish) current of a 100 Amperes (but if you connect the leads with a wire, it will melt and burn you).

For fun i measured my palm to palm resistance just now. It's ~2 mega Ohms currently. So saying i need 50 mili Amps through my heart to stop it, i'd need (V = 0.05 * 2000000) 100000 Volts minimum. But that is for "direct" current (DC, not AC), and it doesn't take a lot of other things in to account. In reality 220 Volts AC could be enough. On the other hand, i know many people survived grabbing the "hot" wire and ground with their other hand, and the only one i vaguely remember died has fallen of a ladder because of the shock.

So in short; Wattage is power, Voltage is.. force, they are used to calculate things involving a lot of stuff (and safety), and the current hurts you because Voltage told it to.

PS Feel free to ask if something is not clear, i misinterpreted your question, something else you want to know or expand upon, etc, etc