This post will show you how to record your screen on mac with quicktime.
1) Open quicktime
2) Goto file > new screen recording
You can now click the screen to record all of it, or click and drag to select an area to record.
Once you have selected the area, or the whole screen, click the record button on quicktime.
Once you finish, click the stop button in quicktime and save your recording.
You now have a video of your screen to upload to youtube, etc