Yeah you definitely need to do more research/reading before you head down this path. Aromasin is an aromatose inhibitor, it works by inhibiting the production of estrogen in the body caused by injecting exogenous testosterone. Some people don’t aromatize much at all and some people do at higher rates. Everyone is different so you won’t know which one you are until you start and get bloodwork. You definitely need to have an AI on hand before starting though, either Aromasin or Adex.
Read through the wiki/links that blvck.scvle posted, there’s a bunch of info you need to learn and get familiar with before starting. Read it several times over and read through the “Ask Anything” threads over at r/steroids and soak up as much info as you can. It’ll start making sense the more you read through it.