AxCrypt is very easy to use and uses 128 bits algorythm. It integrates itself with Windows menus perfectly.
Once installed, if you want to encrypt any file or group of files, you only have to right-click them, choose AxCrypt option and assign it a password.
When you'll need to uncrypt them, use the program's interface or the right-click menu.
Finaly, it also offers a different way to protect files. It can encrypt files and assign them a key file, necessary to uncrypt them when required.