Basically, using Invitt LE only requires entering your invitee's e-mail address in the dialog and clicking Show Screen. Your invitee receives an e-mail including a link. She or he clicks on the link, which opens a browser window showing your screen (I tested with Internet Explorer and Firefox, and both worked). To see it, your invitee must have the latest version of Java (www.java.com).
In my testing, Invitt LE worked as expected, with the screen refreshing fairly quickly. It was a little annoying, though, that my invitee had to scroll to see the whole screen instead of it automatically scaling. And currently Invitt requires both parties use Windows, not Mac or Linux.
(To get geeky for a moment, Invitt LE is actually a simple graphical user interface for TightVNC, an open-source version of VNC [Virtual Network Computing]. More specifically, Invitt LE uses the Java applet version of Tight VNC. Invitt LE adds tunneling for security and an easy-to-use mechanism for inviting others. The LE version isn't a full remote-computer implementation because it doesn't let your invitee use your mouse and keyboard, but the Pro version [$89 per year] does.)
Note: Invitt LE asks that you unblock TightVNC via the Windows Firewall. This is likely not a major security risk, but you should exercise discretion as to whom you invite to your Invitt LE sessions, and use your security software judiciously.