you click the button to set your up the regiment, then you select the skill you wish to use. all skills from fellow pt members will be listed as well. after that seems to be based on timing. from my understanding one person hits the regiment button again? i think :/. if multiple people hit it it resets. well anyways once the swirly lights happen and the chime sounds again hit the skill you selected and the battle regiment should occure. again alot is based on timing and ive only ever done it successfully in a party once. you can do a regiment solo but i dont think anything special happens. but its good practice for the real thing maybe?
It's a bad replacement for the Skillchains in FXI. Which actually required you to coordinate and time your attacks. Then again, this might be asked too much of the hyperkinetics among SE's expanded target audience ^.^/