The checker estimates how long an attacker with a fast computer would need to guess your password, and points out common weaknesses. Your password never leaves this page.
Questions
Is it safe to type my real password here?
The check runs entirely in your browser and nothing is sent or stored. Still, a good habit is to test passwords that are similar rather than identical.
What makes a password strong?
Length above all – four or five random words, or 16+ random characters, from a password manager.