Descriptive Books are used by players to reach brand new ages, and by experienced writers to create entirely new ages. To craft a descriptive book, place leather in the top left slot of a book binder and add either blank paper or pages that you have found. Once crafted, players may link immediately, in which case a new age will be chosen out of the many possibilities. Players who wish to customize their age must add pages that they have found in the world while initially crafting it in the book binder. When using a Descriptive Book, players must be aware of the very high possibility of (Black) Decay in unstable ages. Any form of shifting earth beyond sand or gravel is cause for alarm.
Remember to ALWAYS bring a Linking Book to the overworld before entering a new age. If you forgot to bring a book back to the overworld you will be stuck in the age with NO normal way to get out.
Here are a few tips if you are stuck in an age:
The /tpx command, usage - /tpx <Target player> <Destination player> or /tpx <Target player> <Target Dimension ID> <Target dimension coords X Y Z order>
Note: Must have cheats enabled
You can try to locate a Star fissure in the world which looks like a hole down to bedrock with water at the bottom, jumping in will return you to the overworld.
Another option is to create a Twilight Forest Portal, go through it, and find your portal to the overworld there. Assuming you have one already. (you might need to enable this in the config file)
Edit: Create a Nether Portal going back through the portal from The Nether should bring you back to the Overworld. This method no longer works. Nether portals will not light in created Ages.
Find your character file in your save folder and delete only this file. You will spawn in your map like the first time you entered it. Using this will also delete all of your inventory.
A less stupid way of doing this would be to change the specific world file to an inert name, and use it's name for a "dummy" version of another, less complicated world with an exit portal (usually the nether or twilight forest.) This is done by going into the server files and identifying which "DIMX" file hosts the world you are trapped in. You should then delete or rename this folder, and create a copy of your nether folder (DIM-1) or twilight forest folder (DIM7, usually) and rename the COPY to the previous name of your entrapping world. This will cause you to spawn in the dummy version of the escapable world. Note, however, that you WILL spawn at the coordinates you were at in the trapped world, potentially very high up or in blocks. Have a teleport/waypoint comman at the ready. After escaping to the overworld simply delete the dummy world's folder and voila! You have escaped.
Another possible way to get out of an Age is to use a world editor such as MCEdit to move the player to the overworld.
Another third party program which could be used is NBTExplorer. Using it, you can change your player.dat file directly, changing the dimension entry to 0, that of the Overworld. If you do this, however, make sure to change your coordinates to a safe place. If, for example, you were at a y coordinate of over 200 in your Mystcraft world, you'd then be in the Overworld at over 200 blocks high, which could lead to death. A good idea is to change your coordinates to your spawn.
If you have a mod like TooManyItems or NotEnoughItems installed you could give yourself a linking book or a nether portal item to take you to the nether
You can get a linking book from the creative mode menu.
Use (/give <player name> 90) command to get a nether portal block
The fastest way out is to use the command ( /tpx 0 ). This command will return you to the spawn point of the overworld. Or any other dimension, by passing the dimension number after /tpx
Try to find a star fissure, or go create a Twilight Forest portal as stated before on singleplayer.
The same way can work if you ask the owner of the server to delete your character file.
If the owner of the server shut down the server only then can he delete your player profile.
Have someone else come to the age with a linking book.
If two players spawn an Ender Chest 252, items can link between dimensions. So the player in the overworld creates a linking book and then places it in the ender chest
Do not go to a new age without crafting a linking book to the overworld. You will get stuck.
When you enter a new age a lot of danger awaits: Negative status, landing meteorites, mobs and nether mobs, and spreading decay blocks, to name a few.
This video illustrates how to repair Linking books and Descriptive Books.
This video shows you everything you need to know to use MystCraft effectively.
Make a book binder and put leather in the upper slot and either pages or paper in the centre slot.