Checking the box next to Stay signed in on the Gmail login page will automatically log you in each time you visit mail.google.com. This makes for easier access to Gmail, but if you check your email from a computer that other people have access to, automatically logging in may not be the best option.
When you check the box and log in, Gmail sets a cookie (lasting two weeks) to remember you when you return to the site from the same computer. To disable the cookie, just click Sign out at the top of any Gmail page. You'll need to re-enter your username and password when you return to Gmail.
We encourage you to log out of Gmail at the end of each session to protect the security of your email information. Logging out of Gmail is especially important if you check your email on a public computer. To end your Gmail session, just click Sign out at the top of any Gmail page.