requestWindowFeature() do? I used it to create a custom titlebar, but I don’t really understand what its purpose is.
The explanation provided in the SDK documentation here does not make sense.
Each activity has an associated window (on which the whole UI draws). This window has default way of being drawn (whether toolbar, actionbar, icons are drawn or not).
However, you can use
requestWindowFeature to ask the system to include or exclude some of windows features (toolbar, actionbar and so on).
Here you can find the full list of supported features: http://developer.android.com/reference/android/view/Window.html