Did you slam the doors (probably the rear hatch)?
What's this internet you speak of...?if you don't have an owners manual to read there is this new thing out called the internet in which you can look things up and it actually will give you answers to all your questions. its amazing! the warning light is a master warning light.
If the rear hatch is closed but not fully seated in the latch , it will cause the light (yellow triangle) and beep you describe. Just re-close the hatch and it should go away. Passenger doors that are not fully closed cause the "door ajar" icon (red) to appear .