You have two options for logging in to multiple websites. All you have to do is fill in the complete information or create a new ID-password or make an entry on that website from your Gmail account. For that, your Gmail account is linked to that website. However, after using a website once in a few days, you stop using it or stop using that website. But even then, your Gmail account is linked to that website.
To see how many websites your Gmail account is linked to, you need to start Gmail on your mobile’s Gmail App or Google Chrome. Here you have to enter the Gmail ID-password, to see how many websites are linked. After logging in to Google Chrome, a page will appear. Scroll down to the bottom. View Gmail in: Mobile / Older version / Desktop will appear here.
You have to click on Desktop option. Mail then appears on the desktop. Also all mails will appear. Scroll down to the bottom of this page. Here’s the Gmail information you used. A Details option will appear next to the same information. There you will see Last Account Acitivity, there you have to click on Details. Then click on Security Checkup.
Your saved password will appear at the bottom. Here you can see how many websites and apps your Gmail account is linked to. After clicking on it, you have to click on Go to Password Checkup. Then you need to enter your Gmail ID-password again. Here you will find information about many of those Apps and Websites, where your Gmail account is linked. You can log out of the account by clicking on the side panel from here. When you visit a new app or website, make sure your Gmail account is linked to it.