Microsoft Edge is a web browser (like Google Chrome or Mozilla Firefox) that was distributed with Windows 10 as a replacement to Internet Explorer. Within the last few months Microsoft has released a whole new version of Edge and began applying the update automatically. This action is frustrating many users, but know that you do not have to use Edge and can continue to use whatever browser you have been using.
Automatic updates aside, the new Edge does have some advantages over the old Edge and may be worth trying. It is based on the same code as Google Chrome and you will probably find it quite familiar. You can easily determine if you've received the update by checking the icon: the old Edge was a solid blue lowercase "e"; the new Edge icon looks like a green-blue wave.