A hidden volume can be mounted the same way as a standard TrueCrypt volume: Click Select File
or Select Device to select the outer/host volume (important: make sure the volume is not mounted).
Then click Mount, and enter the password for the hidden volume. Whether the hidden or the outer
volume will be mounted is determined by the entered password (i.e., when you enter the password
for the outer volume, then the outer volume will be mounted; when you enter the password for the
hidden volume, the hidden volume will be mounted).
TrueCrypt first attempts to decrypt the standard volume header using the entered password. If it
fails, it loads the area of the volume where a hidden volume header can be stored (i.e. bytes
65536–131071, which contain solely random data when there is no hidden volume within the
volume) to RAM and attempts to decrypt it using the entered password. Note that hidden volume
headers cannot be identified, as they appear to consist entirely of random data. If the header is
successfully decrypted (for information on how TrueCrypt determines that it was successfully
decrypted, see the section Encryption Scheme), the information about the size of the hidden
volume is retrieved from the decrypted header (which is still stored in RAM), and the hidden
volume is mounted (its size also determines its offset).