Adding a GMail account to the Android emulator is very simple. You do it the same way you do with your Android smart phone.
But what if you cannot add it in the emulator? The common cause for this is that you are using the standard Android emulator. You need to use the Android emulator that comes with the Google API in order to link your GMail account.
If you do not have it, you need to install it. Otherwise, you are stuck.