Telling the time

It's [hour] o'clock. (It's two o'clock.)
It's [minutes] past [hour] (It's five past two.)
It's [minutes] to [hour] (It's five to two.)
It's one o'clock It's half past four
At the full hour (xx:00) we use o'clock. To add half an hour (xx:30) we use half past... .
 
It's a quarter past five. It's a quarter to six. It's twenty past five. It's twenty-five to six.
15 minutes after the hour (xx:15) we say a quarter past.... 15 minutes before the hour (xx:45) we say a quarter to.... Between xx:00 and xx:30
we use ... past .... 		Between xx:30 and xx:00
we use ... to ....