Many of us have dozens of passwords to tens of different services: emails, web forums, workplace computers, games, etc. It is often quite difficult to remember all of them and as a result people use the same password in many services. This is a bad habit because now if your password gets stolen from one service, the attacker gains access to your other systems too. Many people also use very weak passwords, something like "qwerty" or "12345", which are easy to guess just by trying out the most common alternatives.
Luckily there are solutions to these problems: password manager programs. The program saves and encrypts all your passwords behind one master password. That one still needs to be a strong one and you need to memorize it, but after you have set up the system, that's the only password you are ever going to have to remember again. I have been using KeePass and its cross platform version KeePassX. I won't bother writing a full featured review as I just found a recent KeePass review by soft2review, so if you are not yet convinced that you need KeePass, go read it!