Most people use terribly weak passwords, which are easy to crack and very dangerous.
So Mozilla Firefox has offered us some easy tips on how to make
a really strong password to protect our privacy.
Read the information, watch the video
https://support.mozilla.org/el/kb/Choosing%20More%20Secure%20Passwords
and maybe, why not,
you can write a version of this in Greek
to help your friends whose English may not be so good!