Okay it sounds like you are looking for some very basic starting guidance on tyres. Before you make any decisions about tyres (other than to just renew the size/spec you have, which may be your best course), here are the key aspects:
1. Wheel size: R17 or 18. Unless you're planning to change your wheels, you obviously need to stick wiht whatever you have now.
2. Profile: (the /55 bit in 235/55, in the Michelin example you posted). The lower the number, the 'thinner' the tyre (when looked at from the side). Lower-profile tyres will give harsher ride, also make the wheel rim more vulnerable to kerbing damage. Personally on a van I wouldn't go below 55 profile, but that's just me.
3. Tread width (the 235 bit in 235/55). The larger the number, the wider the tyre. A wider tyre doesn't necessarily give more grip, and it will use more fuel. 235 is fine on a Cali, again just IMO.
4. The speed (Y) and load (103) ratings. The load rating is very important, on a van. Calis require IIRC at least a 102 rating due to the weight of the vehicle and 103 is better but it depends on the tyre.
Your insurance will be valid if the tyres are suitable for the vehicle. You'll be safest sticking to one of the options on the door plate.
If you go to a reputable tyre fitter they will sell you something that's suitable for the vehicle. Do you have any particular reason to change from the size/spec you have on at the moment?