Here's a scenarios most of us have faced. Somebody has asked a question about their computer, about how a specific file should be formatted, or how to configure a setting on the OS. You are in a different location, and you would be able to help them if only you could see their screen. There are several options available to you (Go2MyPC, LogMeIn, VNC), but most solutions require a lot of initial setup in order to function by somebody with a lot of technical knowledge.
For this sort of unplanned remote access, there is a website that has done all of that prep work for you, and is offering it free of charge. This website is http://join.me . It's a little different than most websites, you'll notice it doesn't start with www or end with .com. Just have people on each computer go to this website.
Once at the website, have the person whose screen you want to see to click on the "Share" button. They'll need to download and run a file that that button prompts them to access. Once it runs, a small window will appear at the top of the screen with a 9 digit number. You can then type in that 9-digit number into the "Join" box and click the "Join" button. The two computers will sync up and you will soon be able to see and control the Sharer's computer. Once you have finished sharing the computer, just close the join.me window at the top of the Sharer's computer and the applet will uninstall itself.
A lot of people question how something this useful can actually be free. Where's the catch? That's one of the phrases I use to analyze if something is useful or a spyware download. Here's how it works. Join.me is a subdivision of LogMeIn. They are using this simplified version to advertise a more powerful version of the same software. The Pro version includes extra features like being able to switch which computer is being looked at without disconnecting and reconnecting, and also allows up to 250 computers to connect to the Sharing computer for large scale demonstrations.
That can get a little more complicated, but for the basic one to one computer screen sharing, join.me provides a quick, simple access even though no preparation was setup before hand.