Q: When I connect Macbook to External Display, Macbook Resolution Changes

There are two main choice's when using a second display. (Mirroring and Extended Desktop Modes)

In Mirrored or Mirroring Mode, both displays show the same thing. The problem with Mirroring Mode and two different size displays, is that the system tries to choose a suitable resolution for both monitors.

In Extended Desktop Mode, the displays can and should maintain there native resolutions. The problem here is, that you need to learn how to move and manage windows between both displays.

For more, have a look at > Using Dual Displays on Mac OS X: The Experience

and > OS X: How to use multiple displays in Mountain Lion and earlier

or > OS X: Using multiple displays in Mavericks

Sorry, but that behavior sounds like normal to me when one first connects up a monitor.

Have a look at ➤ Video Mirroring in the Mountain Lion article that I posted above.