Go to any auto parts store and get 2 quarts of POWER STEERING FLUID. 1st quart is for flushing out the old fluid and the 2nd quart is for fill up (that's about the capacity of the power steering system on your car). Forget about all ATF stuff in your PS system.
You can check your PS fluid level when cold or hot or running or not running because it will be mostly the same. However it's always safe to check it when it's not running.