What are the steps to turn on mirroring on a MacBook Air?

Go to: System Preferences>Displays> Click on "Display" Tab, click on "Scaled" and they change the res.

This s most likely because of a limitation of the Acer Projector.

Best is to turn of screen mirroring, so at least on the Air you'll have a normal functioning screen.

Let me know if this answers your question.

Boot it up using the osx disk.

This is something called Air Play. To set this up you need to follow these steps:

• Already have or buy an Apple TV version 2 or later.
  
• Have an iMac from mid 2011 or later, a Mac mini for mid 2011 or later, a Macbook Air from mid 2011 or later, or a Macbook Pro from early 2011 or later.
  
• Have a Wi-Fi or ethernet internet connection.
  

Now you have to go through the set up to get the devices to "talk" to each other. You do that by using these steps:

• Turn on your Apple TV and your computer
  
• Go to System Preferences and click on "Airplay Mirroring"
  

After this you can play around and see which resolution size you want your TV to have compared to your computer. It completely depends on your TV and computer, but I usually set it up to match up with my Apple TV since I watch stuff from my computer on my television (it sounds like you will do this too).

This is a very simple solution, fortunately. The default behavior of an external monitor connected to a portable Mac is to act as extra space, effectively extra screen "real estate," where you can move windows or do whatever else you need to.
Verify this by moving your mouse to the right-hand side of your screen, and then keep going - you'll see your mouse appear on the external monitor.

If you want to have the external monitor reflect exactly what you are doing on the primary monitor, simply go to Apple menu > system preferences > displays > arrangement and check 'mirror displays.'

And that's all there is to it!

Go to system preferences and then displays, there will be a check box indicating to activate video mirroring. Click on the check box and what will show is what is showing on the laptop. Hope this helps.

When connected to an external display you have 2 options.
Extended you can stretch across both screens like a giant desktop or you can have mirrored displays which have exactly the same thing on each.
With your monitor plugged in...

1. Open Apple ▸ System Preferences..
2. Select Displays
   
3. Go under Arrangement section
4. Check the Mirror Displays check box
   

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click on the apple symbol

click on system preferences

click on displays

make sure you have mirror turned off. increase the resolution on the second display to higher resolution.

it should detect the max available resolution if you press the detect display button

It is probably mirroring the screens on your MacBook and the projector. If you want different resolutions and things on each screen, go to the Apple menu, System Preferences, Displays, Arrangement and uncheck the "Mirror Displays" checkbox.

Is the mirroring still taking place or just on the one display.  If it just on the Macbook, go to the display settings and select the arrangement button, there should be a mirror button there.