At this moment I have over 100 logins for various online accounts. There is no way I could remember all of those passwords without a password organization tool. The program I personally prefer is 1Password, mostly because of my mac roots, but there are many others such as Keepass and Lastpass.
The way those programs work is quite simple – you have a single master password to decrypt a file that has all of your other passwords. While that may sound very insecure, it is actually the complete opposite. Password tools make organizing your login credentials much easier, and many of the tools include alerts to remind you update your various passwords as well as the master password. They also include generators to create passwords of various strengths and sizes.
The main thing to remember is to have a secure master password – since a weak one is no better than putting your passwords in a plain text file. I personally prefer to use at least a 15 character password made up of several letters, numbers, and symbols which I update every few months. My various login credentials all use long (15-30 character) passwords. This is ideal – since it ensures that no two logins are the same.
Whether you have ten logins, or a hundred, I cannot recommend enough how useful password tools are.