Hi there! Thanks for posting your question up on this page! As an employee at Apple, I will be glad to help you. First, go ahead and open the iMessage app on your Mac. Once that is open and it looks like the regular iMessage screen, look on the top left hand corner of the Mac. There will be a few buttons, from left to right, this is what they will show: The apple logo, iMessage, and Preferences. Go ahead and click on Preferences, then Account, then click sign out. For FaceTime, it is essentially the same thing, open the FaceTime app, look for the button that says "Preferences" on the top left corner of the computer, and from there you will see a drop down menu. Finally, click on Stop FaceTime to turn off the FaceTime on the Mac. Thanks again for posting your question here and let me know if you need any more help! Have fun with your new Mac!