How to use Twist messages in robo-arm?

edit

Hello. We have arm with servo joints,we are writing controller for it, and i don't know how correctly apply Twist messages,to control it.

Some questions:

1)If task is only to rotate angles of servos , i need only "angular" field of Twist?

2) If arm has 4 servos, i have to send 4 Twist for each of them? How should i do this? Arrays, separated topics or otherwise?

3) Twist not used for this tasks and this questions don't make sense.

I will be appreciate any advice. Thank you very much.