If I understand your question, you have two groups of measurements, a Control group, and an Intervention group, where each is assumed to be drawn from a Normal distribution.

You want to measure the mean (average) of each group, and then determine if any difference is statistically significant (it is important to know for your area of investigation just what level is considered statistically significant).

You may get some help from:

http://en.wikipedia.org/wiki/Student%27s_t-test