Statistical Analysis

I have been trying to understand statistics for the past 3 weeks and I don't seem to be getting anywhere at all. I am completely stuck on the standard error of the difference between means when working to calculate a t test for individual groups. The funny thing is that I already had the exam, and I actually passed, but I cannot rest until I completely understand it.

I have tried web searches and reading other sources besides my handy, dandy text book, but so far nothing seems to "click." I can't just skip over this chapter, I need to know what I'm doing. Unfortunatly, the statistical odds of that happening are quite low. I am even beginning to wonder if going back to school was a good idea at all.

I think I am stuck on figuring out the variance for each of the groups. I think I need to do that to calculate the standard error, but I get 0 for the sum of squares.....and 0 doesn't work well in a ratio. I recalculated my results several times, but I still end up with zero. Of course, I am most likely using the wrong numbers, but I can't find any websites that explain the process so someone like me can understand it. The way I figure it, I have to understand the "why" before I can grasp the "how." I definitely do not understand the why of it. I keep ending up with "WHY bother?"

Well, back to beating my head into my statistics book in the hopes that I can beat some knowledge into it.