It is super easy to sign into Formstack. You can sign in with your Formstack account information, OR you can sign in using your Google existing account. If you choose to sign in with Google, you will be prompted to pick the Google account you'd like to sign in with (if you are currently logged into multiple accounts at the same time).
Once you select the Google account you like to use to sign into Formstack with, you will be taken to a screen to grant permission to Formstack to access your Google information.
If you are logged into your Google account, you will automatically be able to sign into Formstack by simply clicking to "sign in with Google" on the Formstack login page.