How to make a sound increasingly louder after some time?

Explanation

First of all, you don't need to place the script inside a sound, place it in the Workspace instead. The reason is that because the script creates the breathing sound and places it in the Workspace and that is because if you go to Line 01, you can clearly see that local sound = Instance.new("Sound", game.Workspace) is there and it creates another sound..

I've tested your script and it works completely fine, all you need do is place the script in the Workspace and you are good to go!

Solution

Now, I'll explain what the script does;

local sound = Instance.new("Sound", game.Workspace)  -- Creates a new sound in the workspace
sound.SoundId = "rbxassetid://2613820616"  -- This is the sound Id that will be played, you can change it's id to whatever sound you would like to play.
sound.Looped = true  -- Loops the sound so that it will play again when it ends
sound.PlaybackSpeed = 1 -- This should be always set to 1!

sound.Volume = 0.3 --Volume for the sound, you can increase it if you like..

sound:Play() --Plays the sound.

wait(7)  -- Waits 7 seconds before going through these next lines of code

sound.Volume = 1 -- Volume will be now set to 1 (Volume increases)

sound:Play() --Plays the sound

wait(12) -- Waits 12 seconds before going through these last 2 lines of code

sound.Volume = 4 -- Sets the volume to 4

sound:Play() -- Plays the sound

Make sure to up vote and select this as the answer if the script works and you've understood!

Here is how I would accomplish this. I'll post some code and explain what it does.

local targetVolume = 4 -- set the highest it can go (max 10)
local interval = 3
local increment = 2

local sound = Instance.new("Sound")

coroutine.wrap(function()
    repeat
        wait(interval)
        sound.Volume = sound.Volume + 2
        interval = interval + 1
        increment = increment + 1
    until
        sound.Volume >= targetVolume
end)()  

so here I increase the sound by a growing rate, and increase a growing rate. It's put in a coroutine so it doesn't stop the script. Reply with more questions, and mark this answer as correct if it works!

The way I think of to increase the sound throughout is using a for loop. Here:

local maxvolume= 9 --set this to whatever you like
local minimumvolume= 1 --same goes for line one
local sound= game.Workspace.Sound --Just an example of the pathway

for i= minimumvolume,maxvolume,1 do
 sound.Volume= i
wait(7)
end

So here, I set some variables to indicate the minimum and maximum volume. I also made a pathway to the sound object that the code is manipulating.

The for loop will keep increasing the volume up to a certain point. Pretty simple script that's easy to understand. s