Timer Things for different uses?

I'm thinking of making multiple Timer things, and so that there would be a SurfaceGui and that the TextLabel's Text property would be equal to the Value in the Model called "Time" and then I would like say that every second that goes it takes away a second from the timer... I know that it's

wait(1)
Time.value = -1
wait(1)
Time.value = -1

but I don't know how to do the thing properly cos as you can see I did -1 but I seen that if a value is added then it's like

addvalue.TestValue = 1

or something like that, so I want to do mine to take away seconds, not add them, and then of course I know this one isn't from the Topic but, how do I get the Model's Position so that it could be used for something, like for example, use the Position to insert into NPC for the Destination, just like in some Zombie Games there are Chickens with C4 and then the Zombies go after them, but that's just an example, so thnx for listening and plz answer.

It's just if you asy the Value is uqual to -1 it will be equal to this number, what you have to do is to say that your new value is equal to your old one -1. This script will help you. Also you can use loops so you dont have to write the same code over and over again. And remember to pinpoint yout "Time" so it leads to that value.

for i = 1, 60 do -- or as much as you like
	wait(1)
	Time.Value = Time.Value -1
end

Use a for loop!

for i = 0, 10, 1 then --If it's a countdown, swap 0 and 10, and change the 1 to -1; you are free to change the end value (middle value) if you want to make it longer/shorter.
       Time.value = i
       wait(1)
end

By the way guys, am also planning to make a thing that would start countdown OnClicked, so it's like a Tool and so you click to drop it, and then the countdown starts, and also I want the Time to be fully in control cos I want the person to be able to set their own time...