I'd just use a walkthrough because there to much stuff to write on this plus you get to know what order to things in.
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When you convince Hercules he smashes the lock for you
After you have the Hades Crown and the Trident from Poseidon, use the mirror to travel to the gate of Olympus (lightning bolt symbol at top). Hercules will smash open the lock and you can enter Olympus.
To get Hades's offering, you go to the garden with the spinx statue. You then find a pomagranate tree and pick them. Those are the offerings.
After Zeus takes the 5 sacred items, you can get Hercules to help you reach the throne rooms of Hades and Poseidon. Once you have the crown and the trident, you can go to battle Zeus on Mount Olympus. Transport Hercules to the gate and he will smash open the padlock. (*before going to Olympus, you will need the drachma coin from cleaning Hades' temple)
You don't get in until you have collected all of the five sacred items. After that Hercules is convinced to help you and he smashes the gate open.