What is a one-sentence summary of the following article?
It's located at https://www.facebook.com/. If you're already logged into Facebook, doing so will open your News Feed. If you aren't logged into Facebook, first enter your email address (or phone number) into the top-right corner of the screen and click Log In. This arrow is in the top-right side of the Facebook page, to the right of the question mark icon. It's near the bottom of the drop-down menu. This tab is in the top-left side of the page. It's toward the bottom of the options on this page. Facebook's desktop site organizes your login sessions by device (e.g., Facebook for iPhone), so selecting one will show you all instances in which you're logged into Facebook on your selected device. Doing so will log you out of Facebook from the selected location on your selected device and remove the item from this list.

Summary:
Go to the Facebook webpage. Click ▼. Click Settings. Click Security. Click Where You're Logged In. Click a platform. Click End Activity.