What is translation mode

Google search tells me its for translating English in excel... I believe it doesnt work like that in SR2. Still, it might be very useful for docking.
Also i was wondering what button enables the velocity changing mode for RCS? Translation toggled on didnt seem to make RCS change my velocity.
So basically:
What is translation mode and how to enable that other mode for RCS to change your velocity instead of turn the ship