MacBooks are reliable computers in general, but they do crash once in a while, and can lose all of your stored data in the process. You can avoid the panic that comes with lost data by backing your computer up regularly. Apple's Time Machine makes this process quick and easy.
Connect an external hard drive to your MacBook.
Click "Use as Backup Disk" when you are asked if you want to use the hard drive to backup your MacBook. Time Machine will then open and backup everything on your computer.
Close the Time Machine window when the backup is complete.