TruCrypt is a nice tool that can encrypt an entire partition or storage device (USB flash drive or USB hard drive). Other persons will not be able to read the data on the device without having correct password or encryption key.
Download Trucrypt and install it in your system. While installation, it creates System Restore point and then install the too, in your system. After installation, run it in your computer.
I recommend all users to read the official user guide before using this tool. At first, the tool seems to be a bit complicated. So, reading manual will help in preventing any kind of data lose.
You will have to create a TrueCrypt volume on removable drive with desired encryption option. After that you can select the password for your TrueCrypt volume and then format it. Now mount your TrueCrypt Volume and use it.
This tool is available for Windows, Linux and Mac Platforms.
Download this tool for free