Breastfeeding QUESTIONS:

I'm gonna be a mommy very soon and I'm curious,
Since the first days of baby's life youll only be giving out colostrum (and I heard baby loses weight sometimes because of the lack of actual milk), has any other mommys given their babies formula on the meantime until their milk finally came in and what would you do? Such as, when would you decide to give them formula?
And does giving them formula also get in the way of getting your milk to come through since your not breastfeeding?
I'm really confused about all this, I know for sure I want to give our baby girl breast milk but I guess it scares me that she'll cry a lot because I'm obviously not giving her milk milk the first few days and lose weight.
Help!