You can create a password that consist of letters, numbers, and special characters.

Be careful in using spaces for username and password. The system will require the Users to enter the username and password with spaces added even if it is the first or last character in the field.

The password you set are case sensitive by default, however, if you don't require passwords to be case sensitive, you need to uncheck the Case Sensitive box in Advanced Option tab during creating a Content Settings.