Usually all your files like phone numbers, love letters, bank account data etc. are stored unencrypted on your computer's harddisk. All the data is accessible for everyone who has access to the harddisk. This is very bad in case someone you don't trust gets your harddisk. E.g. a thief that steals your notebook, or breaks into your house or company. If a thief has access to your disk he/she can also read all the files that where saved on it, no matter whether you have a login password or not - the files are always stored unencrypted and so readable with the right tools.
This software adds a layer between the data you save and the actual format in how the data is stored on the harddisk. This way you need a password to access the files. This is very easy to use without complicated configuration steps. And it doesn't affect your usual workflow.
NAS is an acronym for Network Attached Storage. This means you have a fileserver in your local network, that stores all your data. If you run the CryptoNAS software on this server everything is encrypted and so unreadable for everyone but you.
Maybe you have an outdated PC laying around. Boot it up with the CryptoNAS live-CD. Now you can access it from your workstation with a browser. Then you partition and reformat the harddisk of the old PC with encryption support. Therefore you provide a passphrase. This is all done through the user friendly webinterface (see screenshots). You can also plug in an external harddisk and use this to store your encrypted data. Afterwards you copy your sensitive data over the local network to the old PC which now works as CryptoNAS. All file are now stored on its harddisk in a secure way with stron encryption. Nobody can access your data without the right passphrase.