Most doors have locks on them. Shocking, I know, but they are there for a good reason: to keep people out. It would be nice if we all lived in a Norman Rockwellian world where our doors would never be locked and we would all be busy painting self portraits, but that's not the world we live in.
Sadly, in our world your Mac might get stolen. When this happens bad guys have the potential to get their hands on lots of your information. One easy way to thwart them is by disabling automatic login for all accounts on your Mac. This means that when your Mac boots up you will be prompted by a dialog asking for a password (at the very least, you can change the settings on this dialog, but that is a matter for a follow up post). Not the most comprehensive way to Secure your Mac, but it is a start.
Read on to learn how to do this.