Selecting Layer → New Layer… in the main menu. This brings up a dialog that allows you to set the basic properties of the new layer; see the New Layer dialog section for help with it.

Selecting Layer → Duplicate Layers in the main menu. This creates a new layer, that is a perfect copy of the currently active layer, just above the active layer.

When you «cut» or «copy» something, and then paste it using Ctrl+V or Edit → Paste, the contents of the clipboard are pasted into a new layer.