What is willpower?

How can we put willpower, or whatever it truly is, to work for us?

I believe it is a character trait that one either has or does not have. Those who are strong emotionally and who have good self esteem seem to have the discipline and determination to have self control (willpower). Those who are weak emotionally, have little to no self esteem, tend to not have this discipline.
Take, for instance, those who have addictive personalities. They lack the discipline to say no to a drink, to making a bet, to over-eating, to spending too much money, etc. They lack this discipline because they are weak with little self esteem. They create their own illusion of self esteem by drinking or gambling or over-eating. As long as they are participating in these actions, there is a sense of accomplishment (winning at gambling, gratification by eating, escape by drinking) and this sense of accomplishment creates the closest version of self-esteem that they know.
But we all know that having a healthy self-esteem comes from having a healthy mental relationship with yourself and with that comes the ability to have willpower.

I think it's pretty much the same thing as motivation. Using some of the phrases Georgia mentioned, I'd say it involves self-control and discipline to keep your intentions and strength on something, plus having enough natural foresight to see (feel) that what you're doing could be more than what it seems/feels at the moment you start it. I think most lack of motivation or weak motivation arises due to the feeling one can't meet what one sees down the line (simple stubbourness follows close behind). It takes some strong steps to get into a point where you can feel like you're on the track to doing what you're hoping or wishing to do. The use of movitation is used in all kinds of our daily activities. A good example seems for me to be reading: when I start, I feel more simply starting something that has many pages ahead, yet when I get 4 or 5 pages deep I just began feeling the actual story and I'm motivated by reading the story, not the number of pages left, from there on until I put the book down for the day. One can be motivated to do anything if one only tries to get into it a little more.

Addictive personality is a curious case. Often addicts are very intelligent people. Now, just how clever do you need to be to decide to keep your family, your friends, your job, your health, your home instead of having another drink ? Yet the addict and those on the way to dependency know this and still go on. The evidence is there, in front of their eyes.

It takes real 'willpower' to cast aside the wife, kids etc just to take a drink. That's what I call decisive !

It does seem that when I feel pretty good about myself, I can get more things accomplished.

Unfortunately, in addition to having so many things to do, when I do them, most results are unfavorable. I had to go and become a high risk taker, which sounds nice, but now I have to realize from the start when something is, frankly, a lost cause. Too much misused energy seems to decrease my willpower.

At least, I am resourceful, can get back up into the fight quite quickly, which is saying much.