A familiar of mine has bought a Mac for the first time, and I would like to help him by showing him how to do things, remotely controlling his computer. How can I do that? I need him to be talking to me by phone while looking at the screen, and then me controlling his computer, so he sees the movements of the mouse, etc. Is there any possibility to do that without installing extra software? In case it's not possible, and I (and him) need to install extra software, I would like to know the least invasive way of doing it. He has El Capitan, but I'm in Mountain Lion and would like to avoid updating my SO. Thanks in advance.