GNU fcrypt is part of the GNU project, released under the aegis of GNU.
GNU fcrypt is on the fly encryption. Instead encrypting individual files. You can have entire file systems encrypted.
GNU fcrypt allows you to hide data from a attacker, who has physical access to your hard drive (eg. seizure or steal your computer). Without inserting the correct password, the data must be intelligible and indistinguishable from random data.
It simply writes your data in a encrypted file. Containing the partitions. It is not bootable. You can choose to remember a password, or you can let GNU fcrypt generate a random password.
If you choose to use a random password then the data will be lost when you disable GNU fcrypt or shutdown your computer(If you not have a swap partition). If you have a unencrypted swap partition the attacker can extract the password (random or not) from your hard disk. So if you want to hide data I recommend that you do not use a swap partition. Or use a encrypted swap partition using a random password. You can use GNU fcrypt to do so.
The goal of GNU fcrypt is that in many cases try to force you to reveal the password is useless. Because whenever the attacker try to force you to reveal a password, you can reveal passwords to data that you not want to hide. You can do it many times. The attacker should not be able to prove that you're hiding something from him.
If your computer is on 24 hours a day. So I recommend that you use a random password, this will allow you to hide data telling the truth.
Using GNU fcrypt you will have some resistance who try to censor the data that you have on your hard disk.
If something is not clear to you, or if you have any doubts. You can ask on the mailing lists of GNU fcrypt.
I recommend that you try things with GNU fcrypt, the extent that you learns it from this documentation.