Human society is based, in part, on keeping things secret. Our society (as it is) would fail horribly if everything was publically known. We rely on keeping some information secret to protect our private content. For example, we often protect access services with secrets we call passwords (though if they are simple words then it's unlikely they're very secure). We also use things called cryptographic keys which are large complicated-to-work-with numbers which computers can use to secure information.
If you've been following since we started Yakking then you've probably got some passwords and some keys of your own. Your keys might be things like SSH identities or GnuPG keys. Your passwords will protect things like your computer login, your social media accounts, etc.
As computer users, we have so many of these secrets to look after that you're unlikely to be relying on your own fallible memory. As such you're likely already getting your computer to remember them for you. If you're doing this semi-well then you're protecting all the remembered credentials with some password(s) and/or key(s).
There are many ways of looking after credentials, generating passwords, measuring the quality of passwords, handling keys, policies for retaining and changing credentials, etc. Over the next few articles we'll discuss a number of these points and hopefully you'll all feel a little more secure as a result.