TrueCrypt creates file encrypted containers which can be mounted as a real disk.
It can also encrypt an entire hard disk partition or a device, such as USB memory stick, floppy disk, etc.
Truecrypt encrypts a partition or drive where Windows is installed.
The encryption is automatic, real-time (on-the-fly) and transparent.
With Truecrypt you can use steganography methods inorder to hide entire partitions.
Encryption algorithms: AES-256, Serpent, and Twofish. These algorithms can be used on cascade for more secure results.
Hash algorithms: RIPEMD-160, SHA-512, Whirlpool
Download the exe installer and execute it.
Select the "Extract" option to extract files to a folder of your choice.
Run the TrueCrypt.exe.
For more information about TrueCrypt in portable mode read this official article.
After installing read the quick start tutorial