Truecrypt has one of the most user-friendly GUIs for mounting encrypted volumes or container files. However, if you do need to use the command line, use it as shown below.
To mount a truecrypt volume using the shell, use following command:
# truecrypt -t truecryptfile /media/truecrypt
Enter the password and the contents of the truecryptfile will be mounted into /media/truecrypt
After you are done, you can unmount the truecrypt volume with following command:
# truecrypt -d