These steps are for TrueCrypt files on your computer or on a removable device like a flash drive.
Step 1: Open the TrueCrypt application either from the removable device (flash drive) or from the Applications menu.
Step 2: In TrueCrypt, click on "Select File..."
and locate your encrypted file. Click "Open".
Step 3: Select any number in the slot list on the far left of the window. Click "Mount".
Step 4: Enter your password. Click "OK".
Step 5: A new volume named "No Name" will appear on your desktop or in your Finder window. Store data in that file.
Step 6: When done working with the Encrypted Volume, either click "Dismount" inside the TrueCrypt Application or eject the file by dragging it to the Trash.