Lyn,
Easy first job, go to the home page of this site and lokk under towing law and beginers.
That will give you enough info to be knowing what to look for on your car and van.
The whattowcar and towsure sites are quite good at checking matches but as has been said, only if your car and van are listed.
The match criteria are essentially the kerbweight of the car and the MTPLM of the van. The figures for the car will be in the handbook and on the data plate, usually under the bonnet, and for the van on a dataplate just by the lower outside entrance door, if it is recent, and in the handbook. Do check the max tow fogure for your car too as in rare cases this can be less than the kerbweight!!
The rest is simple arithmetic to ensure you are within the recomended and legal limits for your outfit.
There are refinements to the basics such as the power of your engine and wether it is petrol or diesel but essentially the above covers it.
Good luck and have fun.