You need an Autodesk 360 account to sign-in to an InfraWorks 360 account. If you do not have an Autodesk 360 account, go to the Autodesk 360 website and follow the instructions to create a new account. Use this account to sign-in to InfraWorks 360.
A few users may administer more than one InfraWorks 360 account. Sign-in and sign-out of your accounts using Sign In in the Collaborate section of the Start page.