To start saving what3words addresses you need to create an account. Your saved locations will be available across all your devices. The first time you save, you’ll be prompted to create an account or sign in.
To save a what3words address, simply follow these steps: http://what3words.com/how-to-use-the-what3words-app/?#save
You can find handy step-by-step instructions on how to use the what3words app here: http://what3words.com/how-to-use-the-what3words-app