Passwords should have a good mix of different characters and numbers. There are many free passwords generators and they are simple to use, just generate a password and remember it. But how to remember it? It is simple, basic rule: use pencil and paper! Here is a link to a good password generator: https://passwords-generator.org/
This way it is secure from all kind of technical issues (virus, hackers, power blackouts…). Other ways of keeping logins and passwords information is to have theme stored in a simple text file in the computer and several copies of that file stored on different media (external hard drives, usb sticks, cloud storage).
Passwords managers are programs used for storing logins and passwords, some people find these programs useful while other don’t like the idea of having sensitive information saved in such systems. There are not many free password managers but here is a couple of good programs: https://keepass.info/, https://pwsafe.org/ and https://bitwarden.com/