New ages will be unlocked as you progress.
You have 1 life use it well.
You will be in adventure mode until you have reached the Smelting Age. 
You can dig below bedrock to get to the Neather once you have a bedrock pickaxe.
There are dimensions underneath the Overworld and Neather.
Skill books unlock new skills,dimensions,etc... when you right click with one in your hand.
There is a town building mod installed.
Journey map is locked until the Modern Age.