wachtwoord, dude, I gave you the link to official Tails description on how to use Truecrypt, how can I unambiguify it more? Except if you are using some software called TrueScrypt, I can`t help then, lol Also I won`t teach you how to use Truecrypt itself, I`ll leave it to very good documentation and Mr. Google

I suggest you to install Tails with its built-in installer to USB and configure Persistent volume with built-in configure tool. It is easier and more "official way" than Truecrypt in Tails.