There are several programs that can be used for this purpose, but you may already have one installed without realizing that it can be used for this. Many people use the excellent music and video program VLC Media Player and this can actually also be used to depict what is happening on the screen.
If you don’t already have this versatile program installed, it can be downloaded absolutely free at Videolan.org:
Start VLC and go to the menu Media. Choose Convert/Save.
Switch to tab Capture unit. Change capture mode to Desk in the drop-down list at the top. Set the desired number of frames per second further down. click Convert/Save.
Select the movie type you want to watch Profile. Enter in the field at the bottom where the video should be saved. click Start.
Now everything you do is recorded and saved to your chosen movie file. To stop the recording, open the VLC window and click the usual stop button.