Would you please tell me where "once" should be used in a sentence when it means "some time in the past"? For example which of these sentences is correct: "Once I traveled to another country..." or " I once travelled to another country..."
Please note that "traveled" is AmE spelling, while "travelled" is BrE. Both are correct, but you should choose which one to use and stick to it (unless context requires otherwise, as in transcribing a conversation between an AmE and a BrE speaker).
Please be aware that I'm neither a native English speaker nor a teacher.