Why is the check oil light coming on from time to time
My wives Rav4 oil light comes on for a second while driving and then turns back off.
The light that you see coming on isn't a suggestion to "Check Oil". It is a warning that you have no oil pressure in your engine. The oil pressure in an engine drops when there is no oil in the engine to circulate.
Think about pumping the water out of a swimming pool. As you begin pumping water out of the pool, you might have 50 PSI in the hose. After pumping out 10,000 gallons you will still have 50 PSI pressure in the hose. It is only when your pool is completely empty and you begin sucking air that the pressure in the hose will drop to zero.
The oil in your engine is so low, that when it sloshes to one side during cornering or braking, there is not enough left in the "pool" and your engine begins pumping air to lubricate the engine. Since you seem to be new to the world of cars, I will add that air is a very poor lubricant. An engine can be destroyed in seconds when being lubricated with air.
Please refer to the attached PDF file to see were the oil level should be on the dipstick.