Usb Hard Drive Encryption How Do I Protect My New External Hard Drive?

How do I protect my new external hard drive? - usb hard drive encryption

I bought an external hard drive from New I connect to the network and the USB port. If I the files and folders in existence, how can I protect a friend or to disconnect my hard drive and connect it to your computer and you see all my files? Is there a possibility that can password that nobody can see what it can.
I tried to free encryption software, but that does'nt seem to work. Suggestions? Thank you.