"God" normally has a capital letter at the start if there is only one God ("God" has a capital letter because it is used like a person's name). When talking about several gods, a small (lowercase) letter starts the word.
AncientGreeks believed in many gods, but Jews believe that there is only one God.
God and Goddess
"God" can be either male or female, but when talking about a female god, then the term "goddess" is often used instead.
Used when somebody is surprised or unhappy about something. Some people do not like to use this phrase, as they think this is blasphemy (an insult to God).