Apple's Quicktime Player has the ability to record the computer screen. 

1. Launch Quicktime Player.
   
   
2. Click File and select New Screen Recording.
   
   
   
   
3. A new Screen Recording window opens.
   
   
4. Click the arrow beside the Record button to make sure the correct microphone is selected.
   
   
   
   
5. Click the Record button to begin your recording. You will be prompted with the following instructions. If you are on a computer that has multiple displays, click on the screen you want to record.
   
   
   
   
6. When you are done recording click the stop button in the menu bar.
   
   
   
   
7. Optional: Trim the beginning and end of the recording by clicking the Edit menu and selecting Trim. The interface will change. Drag the ends of the yellow handles to trim the video. Finish the trim by clicking the Trim button.
   
   
   
   
   
   
8. Save your recording by clicking File and choosing Save...
   
   
   
   
9. Choose a location for the recording and click the Save button.