I need help with this gui countdown? (tried almost every tutorial on youtube and the roblox discord)

Hello, you that you are setting the starting value to one and the taking minus x.

This is the correct script:

local number = 600
for x = number, 1, -1 do --third argument is the increment
    script.Parent.Text = x
    wait(1)
end

REMEMBER TO ACCEPT THE ANSWER IF IT WORKED

I have a timer as well and I feel that what you're doing is slightly wrong. Rather than doing

local Var1 = 600
for x = 1, Var1 do
    script.Parent.Text = Var1-x
    wait(1)
end

you should do

local Var1 = 600
script.Parent.Text = Var1
for x = 1, Var1 do
    Var1 = Var1 - 1
script.Parent.Text = Var1
    wait(1)
end

So what this does is it will subtract one from the text and rather than doing do you did just do it like that.

so now it will be 600 and subtract one from it.

or you can do

local Var1 = 600
script.Parent.Text = Var1
for x = 1, Var1 do
    script.Parent.Text = script.Parent.Text - 1
    wait(1)
end

They both work the first one is more for you though.

local num = 600

for i = 1,600 do
script.Parent.Text = num
    wait(1)
    num = num -1 
    print(num)
    end