The pop up window should redirect to a page which looks like the following.
If you already have an ORCID iD, you can sign in now with your ORCID credentials. If you forgot your password try the reset link at the bottom of the pop-up.
If you don’t have an ORCID iD, click on the “Register now” link at the top of the pop-up window.
You can choose the option to login to ORCID with your institutional account (Unity login), but in order to allow you to take your ORCID iD with you through your career you will need a personal account in any case. Later you can link your personal login and institutional account (Unity) login. This will allow you to login to ORCID using your Unity ID if you would like.