Answer:
The assembly was attended by all male citizens of Athens, Councils of 500 was only attended by the Citizen's Representatives.
Step-by-step explanation:
In the past, Athens held the Assembly around 40 times a year. All male citizens were expected to gathered in one place to discuss various issues such as, taxation, war/security, religion and treaties/alliance with other nations.
Councils of 500 on the other hand, was a attended by representatives that were elected from the pool of citizens. They chose these representatives using a lottery system. (It's based on luck rather than through voting)