If you have more than one Google Account, you can sign in to multiple accounts at once. That way, you can switch between accounts without signing out and back in again.

Go to the Google Account sign in page. Click Create account. Enter your name. In the "Username" field, enter a username.

To sign in to your Google Account (or any Google product): Go to the sign in page of the product (for Google Accounts it is myaccount.google.com). Enter your Gmail username (everything that appears before '@gmail.com'). Enter your password.

It isn't currently possible to merge separate Google Accounts. However, if you'd like to transfer your data from one account to another, this may be done on a per product basis. Or, to start using a new product, you don't have to create another Google Account.