Hi. You can use 'not yet' the same way as 'belum'. "saya belum makan pagi ini" to English is "I have not yet eaten this morning". Another example: 'Have you travelled to Australia?' - "Not yet". In sentences where the subject is a person, "haven't (have not)" can be used instead of 'not yet'. 'Have they finished the homework?' - "No, they haven't". There are exceptions to this, but 'belum' and 'not yet' mean the same thing. I hope this helps you.