Learn to talk about time and ask the time in english. When it's "on the hour" we say "o'clock". But only when it's on the hour. In five minute increments, when it's past the hour (up to 30 minutes past) we say "past". When it's before the hour (after 30 minutes past) we say "to". There are 60 minutes in an hour. 30 minutes is half an hour, we say "half past" or "thirty". 15 minutes is quarter of an hour, we say "quarter past" or "fifteen" or "quarter to" or "forty-five".
