When you set up your phone, you added a Google account. If you haven't had a Google account before, this is more than just a password you set up for your phone.
A Google account lets you organize and access your personal information and files from any computer or mobile device:
Other than remembering your password, you don’t need to do much maintenance on your Google account - just enjoy the benefits of your secure, synchronized information. However, you can:
Many Google apps, like Gmail, Chrome, Photos, and Maps are preloaded on your phone. To learn about and download additional Google apps, read Google’s help.
If you’re having problems signing in to your account, read Google's support information.