Transmission fluid was black when I drained it

I was driving down the road and my car just lost power, but was moving slow until it did not move any more. Read a little on it and put a little fluid in it and it wants to go but then drain it from the plug and it was black, but clean no debris in it. Then I put a little more fluid and it still wants to catch gear but cannot seem to put enough fluid in it to catch all the gears. What should I do? People tell me I can put fluid in a place by the brake fluid holder. What do I do?