Apologies are usually related to degrees of formality. すみません is the default and used for the majority of interactions. But depending on the social status or hierarchy, or whatever of the situation it may be inappropriate to just say すみません。You may want to look at a little bit of keego（敬語） if you have more questions . In short, すみません will get you through the majority if your interactions. ごめん is considered casual.

Beside すみません、there is a commonly word ご め ん , it is a apology that you can only use with your friends and family. It is from ご め ん な さ い . Say ご め ん if you are 5 minutes late to meet a friend.