Bad things sadly happen to computers and files. Hard drives crash, files get corrupted, viruses destroy a machine, and the deletion of key data or documents accidentally occurs. It's like getting a flat tire on your car, it's just going to happen and is understandable and excusable. All you can do it pull out the spare tire and change it. Not having a spare tire or not knowing how to change a tire is NOT understandable and inexcusable. Not having your computer files backed up is also not understandable and inexcusable.
There are three main types of backups with advantages and disadvantages to each:
Local backup. Getting an external hard drive for around $50 is a simple way to backup all of your important documents, pictures, and music. This can either be left plugged in constantly with backup software running between constantly and daily or this can be plugged in frequently (weekly) and a backup performed then. This is simple, cheap, and easy. The downside to this method is that you are only protected against computer failure. Natural disaster, theft, or another event that affects your whole house will destroy both your computer and backup simultaneously.
Nearby backup. This method also has you backing up files to an external hard but then you take that backup to another location, like your office or relative's house. Make sure this is a place you can easily and frequently go. Backups made this way often happen about once a quarter by brining the hard drive home, performing the backup, and returned the hard drive to the remote location. This will protect your files in case of an emergency that affects your home but not your entire city. Also, since files are not backed up as recently you may not have valuable files backed up (like your child's most recent birthday party) but you do have everything except for the last few months.
Online backup. There are several companies including Mozy, Carbonite, Dropbox, and even Google and Microsoft that will backup your files to their servers for a small fee (between free and a few hundred per year based on storage size). These options often include software that is constantly backing up your files and have an option to view files online (so you can show off those latest pictures at grandma's house, check your child's homework from work, or quickly put that new song your just bought onto your work laptop). The security and quality of these companies is fantastic, but there will be rare times when an error occurs so you can't get to your backed up files or everyone has access to your files. Also, these are rich targets for hackers to go after but no attack has worked yet.
My professors were always very understanding when a computer crashed a student couldn't hand in an assignment on time. All my professors required was a backup copy of the assignment from the last 48 hours to grant a deadline extension. Computers do crash and it's something everyone has experienced. Losing files to a crash should never happen.
The story above about my professors is true, but I luckily never had to experience it first hand. I have had multiple hard drives crash on though. My wife's laptop once had the hard drive crash at the tech help at the store we bought it at were kind enough to take a week and replace the hard drive and tell us that all the data was lost unless we wanted to pay hundreds of dollars per hour to have a professional recover the data. We politely declined and I was able to recover about 90% of the data a short while later. The last 10% was a sad loss, but it wasn't anything tragic like early childhood pictures or a thesis paper. I had another hard drive die on me a couple of months ago. I went to the same store, bought a replacement hard drive, and simply restored the data from the backup that was made the previous night. I learned my lesson. So has most of the computer industry.
Both Microsoft and Apple have simple tools built into the operating system that now allow for backups to be made frequently, simply, and with lots of great options. My favorite new option is version control that allows you to not just backup a file from how it was at the time of the most recent backup but to go back and look at different versions of the document from 2 days, 2 weeks, 2 months ago, etc. Setting up these tools is fairly straight forward, but most people just don't take the few minutes to do it with the purchase of each new computer. There is no reason not to. External hard drives and cheap and sold everywhere. Online options are plentiful and simple. It's a needed step for any responsible computer user.
There are several terms that you may hear in backup language. Here is the quick explanation of each:
Differential Backup - This means making a full backup of all your files
Incremental Backup - This is looking at what files have changed since your last full backup and just backing up the changed files.