How Do You Refill The Radiator Coolant In A 1995 Mazda Mx6 V6??

There are premixed antifreeze’s and non mixed. So adding water depends on which type you get. I don’t like paying for the premixed because I can buy the water cheaper then what they want for theirs. I mix mine 50-50, there are directions for how much water to add to the antifreeze to provide for the winters you have in your area.
As for adding water, if it is normal maintenance you add it to the coolant reservoir. This should be checked when the engine is warm. If the radiator cap is working as designed it will keep the system full.
If you have had to open the system, or you feel that if may be low, open the radiator cap and add. The problem with this is that it will not bleed the system and the heater may not work. The it this is the case you should find the highest point in the system (sometimes the upper hose to the heater core, other times the upper radiator hose) and add the antifreeze at this point by disconnecting the hose and pouring water in it till it comes out the open part of the system (the radiator cap need to be on for this by the way).
Good luck.