Back in the days of iChat, Apple used to allow us to share our screens or let us take control of someone else’s, and in Yosemite it’s finally bringing the functionality to Messages. Inside the details menu you’ll see a new icon that looks like two overlapping squares. Click on it and you’ll see two options: “invite to share my screen” and “ask to share screen,” which will help when you need to troubleshoot your mom’s iMac. (MacLife)