I have done the same experiment 5 times and they all came out with data that was slightly different but still reproducible. I want to calculate error, but I'm not sure how. Does anyone know?

I find a coefficient from the data and result in 5 points. Do I find the average then divide that by the standard deviation to get the percent error?

Also how do I add errors? I average those 5 points to get one point, but I use that single point for another graph and try to do a linear fit. How do I add the error of the linear fit to the average error?

I am a bit confused.