It really very important to end all your sessions before clicking on cancel button. For this, sign in to your Gmail account by clicking on link www.Gmail.com. Once you have entered in to your mail box, look at the top right corner of the Gmail page. Here, you will find your email address and display photo. On clicking it, you will get an option of sign out next to add account button. If you have completed your work with Gmail account and want to come out if it securely then click on it. This sign out button will close your entire active sessions.