If you want to be really secure online, you should probably have a different password for every single website… but that gets extremely painful to remember. Sure, you can also use Keepass or another password manager instead, but what if you aren’t in front of a computer that has your password database?
You can use the password chart from any web-based computer, and type in two phrases to generate the password. Typically you’d use the name of the site as one, and then your secret password as the other. All of the calculation is done client-side so there’s not a security problem.