How does the American custom work when greeting neighbor?

I am the one moved in to new unit in this apartment but these neighbors that live in this building seems a bit too cranky. I tried to say hi but they just ignore me and walk over me. I don't know why though. I just moved in yesterday so there shouldn't have been any time for me to get an opportunity to offend them. So I was wondering, if I am the new neighbor and would like to get to know my neighbors, how should I do it right? I heard something like bringing baked cookies or brownies to them and say simple hi. Is that true or are there more ways to greet neighbors?