When creating your account, your password must be at least 8 characters and include one uppercase letter, one lowercase letter, and one number.
Each rule is checked in real time as you type during signup. A checkmark appears next to each rule once it is satisfied, so you can see exactly what is still needed before submitting.
That checklist is on the signup screen. If you are resetting a password later, the only rule is the 8-character minimum.