I wanted to access the developer options to enable adb access on Android 4.2 but cannot find it.
How can I enable that?
Once I've activated the menu, how can I hide it again?
Starting with Android 4.2. developer options are hidden by default to clean up the options menu. They're nice for debugging but some overlay options may be very alienating for average users when they're accidentially enabled.
On Android 4.2 and newer, Developer options is hidden by default. To make it available, go to Settings -> About phone and tap Build number seven times. Return to the previous screen to find Developer options.
You see a popup hat reads You are now a developer when it was successful.
It's not possible to hide it again unless you're root and delete this file:
EDIT: According to this answer it's also possible to just delete the App data of the Settings app (com.android.settings, located at Settings->Apps->All->Settings->Clear data).