While it is possible to travel to many different Ages, it is very important to understand that actually traveling to these Ages is a ONE WAY journey, unless you take a Linking Book with you. It is possible to get stuck in an Age, meaning you will not be able to travel back to the overworld.
It is still possible to go back to the overworld by jumping into Star Fissures or via other mods (such as JourneyMap).
Mystcraft is very book oriented and thus requires materials related to crafting books, such as the following:
It is beneficial to have a village nearby with a Mystcraft villager to purchase additional pages and Sealed Notebooks.