Complex sentence: Most of the powers vested in the Governor-General (prerogative powers), such as appointments of political officials, are exercisable only under advice from the Executive Council, because the Governor-General is bound by convention to follow the advice.
Split into simpler sentences: Most of the powers vested in the Governor-General (prerogative powers), such as appointments of political officials, are exercisable only under advice from the Executive Council. The Governor-General is bound by convention to follow the advice.