Step 1: Step 1: Make it "secure"
Then, click on "new image" and type in whatever name you want to save it with.
make sure its set in read/write and in AES 128 bit encriptation.
next, it will ask you for a password, type in your selected password and click "ok".
Step 2: Creation and transfering
2. you will end up with a file named "whateverunamedit".dmg.
3. plug in your USB.
4. simply drag the file into your USB and wait for it to be copyed.
Step 3: Done
to unplug it you first need to unmount your file from the devices part or from the desktop.
the you just unmount your usb and you're set.
Step 4: Usage
first, plug and open your usb.
then, open your .dmg file. it will ask you for your password so just type it in and you will see a new device (just like the usb) with the name of your .dmg file.
next, open these device and copy your files in there.
to safely take it apart from your computer, repeat step 3.