How do I make a gui timer ....??

I ll give an example

for i = 10, 0 do --we start at 10 and go down to zero by increments of one
print(i) -- we print i so we see whats its value
wait(1) -- waits 1 second then prints its value
end -- finish with an end 

@yurhomi10 That's right but it isn't recommended, use this instead if you want:

local counter = 0 -- The time will start at this second, you can change this to 5 or something else =)
local max = 20 -- The time will end at this second, you can change this to 30 or something else too!
while counter < max do
    counter = counter + 1 -- It will increase the counter by 1, you can decrease it just using the minus
    wait(1) -- Wait 1 second before increasing again
end