Hi

I'm pretty new to this kind of thing but I have a question about the actual speed of spacecraft.

Is all speed of spacecraft measured in space relative to the things we consider to be "still" (i.e the solarsystem) or is it measured to absolute "stillness"? If so, how do you stay completly still in space if its even possible.

Another question is, since the galaxy is moving and spinning, would it be possible to "break" a spacecraft in order for stars etc come to you? That would mean to decelerate instead of accelerate which in my mind anyways seems more efficient but I'm probably wrong

Many thanks!