How to use laptop monitor and external monitor at same time?

most of the time you just have to hit the little button that says fn, and one of the F1, F2, F3,...... keys at the same time. On dells it is the button that says CRT/LCD in blue, on other computers it is the one that shows a picture of a monitor......you can find out from there!

Each manufacturer is different. There is a key combination that allows you to switch between each monitor, or both monitors simultaneously. Read the quick start guide.

This depends on the laptop and the operating system. I'm just going to assume that you're running Microsoft Windows XP. Usually, if you just plug the external display into the external port of the laptop, it will simultaneously show the same image as would be on the display of the laptop. Beyond this, the properties of this can be accessed by right-clicking anywhere on the blank portion of your Windows desktop and selecting "Properties." Click the "Settings" tab. Under "Display", click the drop-down to find and select the output representing the external monitor. Uncheck the item "Extend my Windows desktop onto this monitor", then click the "Apply" button. You should eventually see the same image on both the external display as well as that of the laptop. Click "OK" to save the settings.

plug it into the back

Check the manual. I happen to have a Compaq, an hitting Fn-F4, I can switch between internal LCD, external monitor, and both. Good luck.