Do you know what this phrase mean? "in 900 europeans believed the world was their oyster"

the discoverers and explorers: 1. natives showed jedediah smith the way. 2. william sublette was the first cross it with a caravan. 3.joel walker and his family were the frist settlers to use it. the jumping off point: 1. founded in 1827 near where the missouri river flows into the mississippi. 2. by the 1840's, it was the most popular "jumping off" point for pioneers to stock their wagons with supplies. 3. missionaries from the church of jesus christ of latter day saints attempted to make independence their zion, or holy capital. the route west: 1. the first emigrants to oregon came by ship before the trail was established. 2. ships continued to to travel to oregon even after the overland migrations began, but they were not popular among the pioneers. 3. the fare for a sea journey to oregon was quite expensive--few pioneer families could afford it. i don't know the other three i'm sorry.