Who can explain this script to me?

Hi...

function lightOnFire(part)--This script is creating a function to light something on fire
    print("Going to light this part on fire:") --this helps check is script is efficent in output
    print(part.Name)--same here

    fire = Instance.new("Fire")--Now we are going to make the fire
    fire.Parent = part --the parent of the fire is part we made the part varable with out function up here
end

firePart = game.Workspace.FirePart--There has to be something in workspace called FirePart

firePart.Touched:connect(lightOnFire)--if this firePart was touched the function above will activate

function putOutFire(part)--Now we r going to put out fire
    print("Got to put out the fire on:") --checking in output
    print(part.Name)--same here

    fire = part:FindFirstChild("Fire")--we r finding the parts child which is fire
    if fire then
        fire:Destroy()--we destroyed the fire
    end
end

waterPart = game.Workspace.WaterPart--You must have something in workspace called WaterPart
waterPart.Touched:connect(putOutFire)--Now when touched we are activating the putOutFire function

firePart.Transparency = 1--now both of these r invisible
waterPart.Transparency = 1

Now idk if the script u got works but this is how it works

A function is a block of code that can be executed later. In the function lightOnFire, part is the argument (aka parameter) to the function -- a variable that you can change each time you call (use / execute) the function.

lightOnFire prints two messages, then creates a new Fire object and adds it to part.

lightOnFire lights a part on fire

firePart is defined to be some part in the workspace called FirePart. It's the first thing that's supposed to be on fire.

firePart is the source of fire

firePart.Touched is an event. When an event happens, you can respond to that event by connecting to it. This line attaches the lightOnFire function to this event -- whenever the event happens, lightOnFire happens, and its argument part will be whatever touched firePart.

things that touch firePart will get lit on fire ( lightOnFire)

putOutFire is almost the same. The only difference is that the objects that touch waterPart might not already be on fire -- so you have to check if there is any fire before you try to remove it. (Really this check belongs in lightOnFireToo so that you don't re-light the same object many times)