How does trim work

How does trim work
suppose on my flight plan I keep drifting right like .1 every few second (30-40 seconds) what do I do with the trim then do I turn it left or right if so how much???
Thank you
suppose on my flight plan I keep drifting right like .1 every few second (30-40 seconds) what do I do with the trim then do I turn it left or right if so how much???
Thank you