Using cftool- moving avearage for smoothing

Hi,

I'm trying to use cftool and smoothing my data set using moving average method.

I do not have much of a theoretical background of moving average method.

My question is:

1)I have read the X data and Y data from an xls file and am using moving average for creatinmg a smooth data set.Now, by defauly span is set as 5- which means number of data points used to create a smoothened data set.Does it mean that greater the span more accurate will be the result?

2)Also- does smoothing apply to the whole data set?I mean if I want to smoothen initial few points of my data set (not all points in the data set), can this be achieved?

Shalini