Sometimes when you click on the edit icon because you want to edit a page, you are not able to open the webpage. This is because someone else was editing the page and did not press the save or cancel buttons, but instead just left the page altogether. The purpose of the “check-in, check-out” feature is to stop other people from editing the same content as you at the same time.
If you need to edit a page that is checked out, either you or the admin can just go to the backend control panel at www.yourdomainname.com/administrator and go to System>Global Checkin and all items on the website will be checked in, leaving you or anyone free to edit an item.