Standard Deviation and Varians

I first of all apologize if this is the wrong category. This is for a Statics class at college level, but basic statistics.

I am really having a hard time and confusing myself when it comes to the standard deviation and variations. The formulas (do the best I can without the keys needed on the keyboard) are:

O2m = O2 squared / N - this is variance

Om = this is standard deviation (standard deviation / N squared = standard deviation)

When given a problem are we be given one or the other to calcuate and then continue with the rest of the steps. For example if I am given the standard deviation of 8 and my N = 10 then 8/10 = .80 so this would be my standard deviation.

Would I also then calcuate a variance or or is that only if you are given the variance in the problem you would then use the formula to determine your variance.

This is the only part I am having a really hard time grasping. Ugh.

Thanks for your help!!