What does the Coeff for xcorr actually do?

I am using xcorr to find the cross correlation of 2 timeseries for a tracking task. So one is the pre-determined timeseries of the moving target and one is the person's trajectory. I don't quite understand what the Coeff does to normalize the data. Any help or clarification would be so helpful.

Also, I would like to limit the direction of the shifts/lag, so that the person's trajectory is only shifted to the left to get the max cross correlation. Any suggestions for how I can do this?

Thank you in advance for your help!