This phrase is indirectly comparing a conversation to a map or journey.
If we imagine the rest of the dialog, 2 friends are throwing a party and are still planning it. They need to pick a location and time, invite guests, and bring food. If they were following a map, they might start at a house then follow a road to the store then walk a path to the park. Once they do one thing, the next thing follows.
If the conversation were a road, it has taken them to the next topic for discussion, in this case planning what to bring.