In the old school systems you need to configure a jumper on the motherboard to choose between different hardware configurations.
Later improvements let you make some of those same configurations options in BIOS menus.
Most recent systems - and that includes the Asus N53Jg - will handle that automatically without the need of setting jumpers or making changes in the BIOS settings.
In the case of your Asus N53Jg it has the NVIDIA Optimus feature. BOTH GPUs will be in an active state and the active GPU will be chosen by the system based on the video workload demand.
For all basic 2D office/school work the Nvidia GT 415M discrete video card will be powered down and the system will use the Intel HD GMA which is the onboard GPU included...