Complex sentence: Outside the Cabinet there is an Outer Ministry and also a number of Assistant Ministers, responsible for a specific policy area and reporting directly to a senior Cabinet minister of their portfolio, which serve as the full Commonwealth Ministry of the government of the day.
Split into simpler sentences: Outside the Cabinet there is an Outer Ministry and also a number of Assistant Ministers, responsible for a specific policy area and reporting directly to a senior Cabinet minister of their portfolio. The Cabinet, the Outer Ministry, and the Assistant Ministers collectively form the full Commonwealth Ministry of the government of the day.