There are plenty of tools across the internet that will help you generate random passwords. I recommend using a password manager, and many password managers come with a password generator built in. I've recommended one above in the "Tools" section of this guide. These are generally reliable for creating secure passwords. As a guide, an 8 character random password usually takes a few days to crack whereas a 10 character password takes years. Obviously the more characters you use the more secure the password assuming it is completely random.