When the computer and projector are powered on and connected, both should display the same image, although many times the laptop will need to be mirrored manually.
This can be done in a few different ways, the most straightforward of which is by holding down the Function key (aFna on the bottom left of the keyboard) and pressing the F# key at the top of the keyboard that corresponds with opening the VGA port.
The F# key used will vary from computer to computer (F7 and F8 are most common), but you can tell which one to press based on the images on the key.
Some common ones to look for are:
Alternatively, you can right click on the desktop and open aScreen Resolutiona or aGraphics Properties.a From this menu, you can adjust the screen resolution and/or open the VGA port for the second display. The wording and look of the menu will differ from computer to computer, but this is one example:
The optimal screen resolution to use with classroom projectors is 1024x768. Once this has been selected, if the laptop still fails to mirror, you can select the menu item aMultiple Displaysa or aClone Displaysa to try to open the VGA port
Choosing aApplya or aOKa will accept any changes you have made to the menu and open the VGA port to mirror the laptop.