2002 Cyr Concorde 3.5, after turning off the car, the coolant fills the reservore, why?

Everything you are describing is pretty normal, the temp going up then settling, that's when the thermostat opens and allows the coolant to circulate through the radiator. The coolant filling the reservoir after the engine is stopped is normal because the water is no longer circulating and is still drawing heat from the engine, it expands and has to go somewhere so it goes into the reservoir.

Your only problem I see is the reservoir, it is either too small for the quantity of coolant required for your 3.5 or it is the correct size and you have overfilled your cooling system. The reservoir should have LOW and FULL markings on it (if it is a direct replacement for OEM) and it should be no higher than the FULL mark when the engine is "cold". If there are no markings be sure the radiator is full when cold and then fill the reservoir approximately halfway and see what happens. If the system is working properly and filled correctly, you should have no overflow from the reservoir when the engine is stopped.

The resevoir is there to accept the overflow. When you turn the car off, the engine is still hot and forces the coolant into the resevoir. Wait a while and it should go back down. There should be a mark on the resevoir for how full it should be when cool. Do not overfill.

This is not abnormal behavior.