aromatase is responible for the producttion of estrogen, so an aromatase inhibitor will block the production, aromatase can convert testosterone in to estrogen so if you block this process it can leave more testosterone avalailable.
Aromatase inhibitors are you usually only really benficial if you are boosting your test one way or another. There are also side effects on high doasge of aromatase inhibitors, so try to stick to the dosage or at least no more than 2x.