The most popular use for encryption is to hide large numbers of files, or to encrypt whole sections of a computer's hard drive and keep it safe from prying eyes. This form of encryptiong, called "whole disk encryption," is so popular that it's used as a selling point for the commercial versions of popular encryption programs – especially PGP. The freeware "basic" version of PGP allows you to encrypt email messages and single files, but you can't encrypt entire sectors or folders of your hard disk. Of course, you could pay for the official commercial version of the program, which includes whole disk encryption among its features.
For people who want to encrypt numbers of files, but can't afford expensive encryption programs, Cryptainer is a solution that's not perfect, but works quite well. Cryptainer is a disk encryption program that allows you to encrypt entire sectors of your disk, or your whole disk; however, it's also a commercial program that costs a pretty penny to purchase.
But, as a promotion for its encryption software, you can also download a freeware version of Cryptainer (Cryptainer LE, or Light Edition) that allows you to create encrypted disk sectors. These sectors are treated as entirely separate disks on your system, and you can move files in and out of these encrypted disks. The freeware version of Cryptainer only allows you to create an encrypted disk up to 25 megabytes in size; for larger disks than that, you'll need to purchase the commercially available program. However, you can create an unlimited number of 25-megabyte encrypted disks. Cryptainer LE doesn't have an expiration date. 25 megs may not allow you to hide large audio and video files, but it works great if you want to hide certain documents (such as password files).