How do you constantly add numbers to variables?

There's 2 issues with this. First, you're redefining n as 0 each time the loop restarts, so any changes to the variable wouldn't affect the next loop. Second, you're never adding onto n, simply printing what n+1 would return, which doesn't change the variable itself. Also, you may want to add a wait() at the end of the loop to prevent it from freezing roblox studio.

n = 0 --this creates the variable and sets it to 0 once
while true do
    n = n + 1 --redefines n as n+1
    print(n) --prints the new value of n
    wait() --stops the loop from freezing
end

that's an infinite loop, you need to use wait

Use this code

local n = 0

while true do
    wait(1) --  change it to set the speed with which it increases
    n = n + 1
    print(n)
end

You could do it like this using a while loop

n = 0

while(n <= 20) do
    print("Value of n is: ", n)
    n = n + 1
    end

The above code prints from 0 to 20 until reaching 20 and it will no longer be true.

or using a for loop:

for i = 0,20,1 do
    print("value of i is: ", i)
    end

Above code also prints from 0 to 20.

You have the right idea but there are a few problems in your code:

1. You need to add a wait to your code so that the computer will wait a bit between adding 1 to n each time

2. You need to add the line n = n + 1 so that each repetition of the code the value of n will increase by 1.

3. Put the n = 0 outside of the loop so that n will not be repeatedly reset to 0

The finished code should look something like this:

 n = 0 --the starting value for n
 while true do wait (1) -- the loop will repeat once every second
 n = n + 1 -- increases the value of n by 1
 print (n) -- prints the value of n
 end