We all use passwords every day (well, or have passwords stored somewhere that get used). Gmail, Instagram, Facebook, Tumblr, and on and on all have their own password. What's that, you're using the same password? That's not a good idea, and here's why. Someone breaks into your Gmail with your username and password. Now, they start attacking some of your other accounts using that same password. You've pretty much given them a master key to your digital life if you do that, so let's look at how we can fix that, shall we?
But Xanny, I have 20+ websites, I can't possibly remember passwords for all of them! No one expects you to be able to. Software to the rescue! I'll go over what I'm using, and I'll also highlight something a bit easier to use as well. Personally, I use Keepass as my password store, the Kee Firefox plugin and Keepass2Android on my phone, all of which are free. Think of Keepass as your vault, where all of your usernames and passwords are going to live. Kee, the plugin, communicates with your Keepass to allow Firefox to autofill login information, and Keepass2Android allows you to open your password database on your Android phone. The beauty of Keepass is that you can store the database (it's a single, encrypted file) somewhere and access it from multiple machines. I have mine stored on Google drive so I don't need to worry about it getting out of sync on another machine.
If setting up the above seems to be a bit too geeky for your tastes, there are a few other options. Dashlane, Bitwarden and Lastpass are all cloud-based password storage options with their own browser plugins and phone apps. I've used Lastpass myself, however, they've had some security breaches in the past so that led me to giving Bitwarden a try. It worked pretty well for a while but eventually I just wanted to make sure I had all of my passwords locally and completely under my control, so I switched to Keepass. Of the three, Lastpass is still the most popular, but all three are pretty easy to use and set up.
The main point I want to make: Please, use different passwords, no matter which way you decide to store them.