What are the key differences between Class C and Class D airspace?

I'm studying airspace classifications and I keep mixing up Class C and Class D. Can anyone give a practical summary of the differences?

In Australia, Class C airspace typically surrounds major airports and extends to higher altitudes. You need a clearance to enter, and ATC provides separation between all IFR traffic and between IFR and VFR traffic. Class D is around smaller controlled aerodromes. You still need a clearance to enter, but ATC only provides separation between IFR aircraft — VFR aircraft receive traffic information but are responsible for their own separation from other VFR traffic. Both require two-way radio communication and a transponder.

So in Class D as a VFR pilot I need to keep my own lookout more actively?

Exactly. In Class D you'll get traffic advisories, but the responsibility to see and avoid other VFR traffic is on you. In Class C, ATC actively separates you from IFR traffic, which is a higher level of service. Always check the ERSA and charts for the specific dimensions and requirements of each airspace you'll be flying through.