Recently the National Center for Biotechnology Information (NCBI) implemented a requirement to link My NCBI accounts to a third party such as a Google, a university/institution, or a login.gov account.
When you try to log into your My NCBI account you will be prompted to link it to one of those logins.
For more information on the options available and the process see the FAQ on the NCBI Insights blog at: Important changes to My NCBI accounts
My NCBI accounts personalize your experience using PubMed and a few other NLM databases.
You can save searches, create alerts, view your search history, create collections of citations, create your bibliography and create your CV using the SciENVcv application.
Details regarding this change and other information are in the NLM Technical Bulletin from earlier this year: NLM Technical Bulletin