LogMeIn uses a small app, installed on the user's computer, that allows remote support to take it over. The user is usually provided with a six-digit code from the support technician and he can then install the app and initiate a remote session with that.
After support provides the PIN number, the user can then use this on the web page. This allows him to download the app and is then connected to the session that was prepared by the support technician.
In addition to the PIN option, the support technician can also email a link or send an SMS. Various operating systems can be supported including those for most smartphones.