What was the purpose of the bridge (Or was it just for crossing sides?)

Connected the 2 sides

They wanted to build an indestructible bridge that won't collapse in an earthquake so they built Golden Gate bridge it's a suspension bridge in case of an earthquake it will move and shake but won't collapse And ofcourse to connect the 2 sides there's 3 more bridges connects the 2 sides

Yes to connect two sides

To connect with the island

Crossing sides and I suspect now it's a tourist attraction and money maker for the city.