Monks do not use energy, they use jin. In place of the energy on all ui's even the default, is the jin bar. This does start out at 0 on all monks, and wil raise depending on what skills you use in combat. Some will gain 1 point of jin per hit, while others will gain more as you level up and get higher skills.
Your total amount of jin you can have depends on your level. It does raise each time. I have a level 14 monk and hers can (i think) raise to 12. At level 5 it was only 8 max.
In unison with this, some skills will also take jin away as well. Most of your finishing skills and specail attacks will take jin away from that pool you have built up. Mind you, if you are in active for a small amount of time, that jin can drop back down to 0, untill you enter combat again and start to build it up.
Most ui's will show you the total jin you can have. So like for my monk and my ui, it will display 0/13 with no jin gained. The bar will be empty, untill i enter combat and start building it up again. The bar will move up as will the number.
I hope that answers your questions you had. If not please feel free to let me know. I can log onto one of my characters and get you the exact skills that will gain or use jin.