How do i do 3 while true do loops at once?

As I said earlier, adding another spawn should fix this. I did forget to mention that you had to use the spawn before your final while loop.

Spawn(function() 
        while wait(5) do 
            print("5seconds")   --Prints "5seconds" every 5 seconds and "0.1second" every 0.1 second
    end
end)

Spawn(function() 
        while wait(3) do 
            print("3seconds")   --Prints "3seconds" every 3 seconds and "0.1second" every 0.1 second
    end
end)

Spawn(function() -- keep the program looking consistent, and in case you need/want to do something AFTER this part of the script
     while wait(1) do -- I changed this to 1 btw.
            print("1second")
    end
end)

coroutine.resume(coroutine.create(function()
while wait() do
--first loop
end
end))

coroutine.resume(coroutine.create(function()
while wait() do
--second loop
end
end))

coroutine.resume(coroutine.create(function()
while wait() do
--third loop
end
end))