The Internet is a great resource for learning but some information is more accurate and some less so. You have to cross reference and test what’s provided to make sure it is real.
You can get the effect of off camera flash with a reflector held a couple of feet from an on camera flash. You can use a real photographic reflector or a sheet of white foam core. The catch for using either is the need to hold the reflector at the right angle to reflect the flash onto your subject.
Most Nikon and some Canon models can fire an off camera flash using the pop-up flash. Canon just introduced the 600 EX RT which has a built in radio but another 600 EX RT or a dedicated radio is needed to fire it, off camera using radio. Like other models you can use a pop-up or another flash with commander mode to fire it, using light. Some other makes of flash can be fired when they see light from another flash.