Driving Car with Trailor Law? Trailor upto 750kg i'm confused about?

My licence was passed in 2005. It says B and B1 on my licence. Searching on the.gov website it says i can drive upto 3.500kg vehicle and a trailer upto 750kg.

does it mean trailor itself 750kg max of a trailor and whatever loaded on it to a max of 750kg?

so if i drive a ford transit thats approx 2000kg, and my car trailer is 650kg empty, and i have a car on the trailer thats an audi A4 at 1,600kg will i be able to do that on my licence or have to pass a separate test?

I'm sure that the GVW of the trailer would be 750kg. That would be the total weight of the trailer and load. I wouldn't make any sense to let you pull what ever you want on a 750kg trailer. You could have 20,000kg on it.

The 750kg is the maximum mass of the laden trailer, as stated on the trailer's weight plate.
Your 650kg unladen trailer probably has a maximum laden mass of around 2500kg, so the trailer isn't within the 750kg limit whether laden or not.
You can tow a heavier trailer provided the total maximum laden mass of the tow vehicle and trailer do not exceed 3500kg, but what you are proposing is a van with (probably) a max laden mass of 3500kg, leaving you little or no margin for a trailer.