All of us have at least 10 or more accounts on the net nowadays and managing all those passwords can get tricky if not done correctly.
You can easily forget your password and if you don't you have a very easy to guess password, and that is a very terrible thing to do.
You also have to remember other information like credit card informations, licence keys, secure notes etc.
A simple solution to those problems is a password manager.
A password manager creates a database of your passwords, username and other details. Those passwords could then be easily synced across your devices and with things like autofill they make the whole online experience much more simpler to everyone without worrying about a gazillion passwords. You do have to remember the master password for your specific database and that's a necessary evil.
A good option is KeePass it has both online and offline capabilities and is completely free. KeePass is available on all the major platforms including Windows, Android, Linux, Mac OS, iOS, Firefox, Chrome etc.