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.

Go to http://accounts.google.com/signin/usernamerecovery and enter any email accounts or phone numbers that you've had for a while and which may have been used as recovery info. The “find your email” page can help you locate any forgotten Google accounts. On the next page, you'll be asked for your name.

Most websites' or services' login pages can be accessed by clicking a Log In or Sign In link somewhere on the home page (usually in the upper-right corner). Then you'll enter your email address (or other types of username) in the "Email" text field and your password in the "Password" text field.