system
Given the following post, respond as if you're commenting on Reddit:
human
How do you calculate velocity in space?

Do you use Earth or the Sun as a frame of reference? Is there some way to find out how fast they are moving through the universe? 

How does the speed of our solar system affect time? If you found a way to come to a stop (with respect to all of existence), would the traveler age faster than everyone else on earth? Would the earth appear to move away slower?

Disclaimer: I am not really educated in any of this, barely have any knowledge of relativity, just curious.

Edit: Would it matter which direction you started moving? For example: moving away from Earth in the direction of the expansion of the universe would increase your true(?) velocity, while moving toward the center would decrease it.
gpt
You can use any reference frame you like, there is no absolute frame of motion in the Universe.  If we measure the orbit of the planets, then the speed is in relation to the Sun - but if we measure the orbit of the moon, then the orbital speed is in relation to the Earth. The speed we measure Voyager travelling at, is in relation to the Earth, which is why on sites such as NASA the velocity report of the Voyager crafts change in relation to where Earth is in it's orbit - in reality the Voyager crafts are travelling at a constant velocity.  
  
We wouldn't know if we had truely "stopped" in the Universe, as there is no outside, or known centre to measure our Velocity - we would just know what our velocity/motion is in relation to xyz coordinates of whatever we decide to measure our velocity against.