when you workout you are accomplishing 2 main things
1. training your body to react to what you are doing (if you ever worked out with a newb you will notice they are struggling while you are smooth because you have been training for years and they haven't)
2. breaking down the muscle (yes this happens, you don't grow while you workout
if your body is not used to this then of course you will get sore as a reaction. soreness is your body freaking out and wanting to repair what you just put it through. once it is conditioned it wont' get sore as much until you shock it and change up your workouts.
as far as pumps those are your body shuttling in blood and nutrients into the muscles again as a reaction.