The backstay is used to bend/unbend the mast
. a short version, when sailing with the wind
from aft - the backstay should be loosened to allow the sails
to become fuller.
Beating up against the wind
or on a beam reach the backstay is tightened to make the sails
flatter and provide more tension on the front part of the sail.
Yes we do make these adjustments while sailing, not just in port.
There are no stupid questions - just a desire to learn