I don't understand why functions are used can someone explain?

Hello,

This is a bit advanced , but it is a good explanation.

function hookmake ()
    local hook = Instance.new("Part")
    hook.Name = "Projectile"
    hook.Anchored = false
    hook.CanCollide = false 
    hook.Transparency = 0
    hook.BrickColor = BrickColor.new("Dark stone grey")
    hook.Material = "Metal"
    hook.Size = Vector3.new(0.75,0.4,0.4)
    local hookmesh = Instance.new("SpecialMesh")
    hookmesh.MeshId = "rbxassetid://1321670738"
    local hookatach = Instance.new("Attachment")
    hookatach.Name = "RopeAttachment"
    hookatach.Visible = false
    hook.Parent = game.Lighting
    hookmesh.Parent = hook
    hookatach.Parent = hook
    hookatach.Position = Vector3.new(0,0,0.3)
    return hook,hookmesh,hookatach
end -- This is a function I made.

My question is would you write all that everytime you need the specific instance or just call the function?

The answer is obviously you will call the function everytime you need it.

hookmake()

In your case, it is a simple script.

function lightOnFire() 
    print("Lighting on fire!") 
end

The answer is obvious you would not want to write print("Lighting on fire!") everytime you need the desired ouput. Just by calling the function it will output. lightOnFire()

Function is a way to make life easier. In life everything has a function and it is the same in programming.

Thank you for reading.

Feel free to ask any questions.

PS : Your other solution.

t = 0 -- time
while true do wait(.1)
    t = t + 1 -- 1 hour in the game is 1 minute in the real life.
    game.Lighting:SetMinutesAfterMidnight(t) -- Keeps the time cycle going on.

    if game.Lighting:GetMinutesAfterMidnight() == 18 * 60 then -- This is 1080 minutes.
        print(game.Lighting:GetMinutesAfterMidnight())
    end
    if game.Lighting:GetMinutesAfterMidnight() == 6 * 60 then -- This is 360 minutes.
        print(game.Lighting:GetMinutesAfterMidnight())
    end
end