Write in game, save it on a .txt and after read it in game again.

I don’t know how to make a script that allow u to write in game something, then save this in a .txt and after when u want it allow u to read what u wrote before and u could rewrite again. To make a example: Like a book wher u can write save it an later read it and if u want repeat the process many times u want. If u need more information ask me and I try to explain more. thx

Search for how to read and write data to a text file.

Use a UI.InputField to enter the message into.
Save the InputField contents to playerprefs.

Then you can load the message from playerprefs into the UI.InputField if you want to edit it and save it again etc. etc.

http://docs.unity3d.com/Manual/script-InputField.html

^ don’t do this way. Playerprefs are not a viable way to save.

Rubbish!

Explain why, given the information provided by the OP, that PlayerPrefs wouldn’t be an acceptable and easy option in this instance.

Why do so many people jump on the don’t use PlayerPrefs bandwagon when it is suggested to use it?

I’ve used PlayerPrefs in most of my games. The only time I wouldn’t would be for a multiplayer game where players could access data to their own advantage and to the possible detriment of others. In a single player game it really doesn’t matter!