Screencasting is the Term Used When Something on Your Screen is Videoed and then Broadcast as a ScreenCast
Part one of the following video was a free 15 second download I was given by a commercial company (they licence its use provided it is part of a longer video).
The rest of the video is a screencast where I used a tool produced by Google that demonstrates the role of different platforms for driving traffic to websites. The content of the video is not the important part here. It is the way I've been able to show my screen as a video and then post it wherever I want.
Several free pieces of software exist that are capable of doing this. Some of these do contain adverts and prompt you to buy the commercial version. However they are free and most of them work quite well. I suggest you search for "open source screen capture software" and make your own decision.
In my own case I started with a free software system but then upgraded to the full cost version.
Another thing to note with this video is that I used a free recording and editing suite to record and edit the audio. Plus the background music was free.
I'll explain more about that in another post.