Roblox Kill Others Gui Script? i keep having trouble and know no lua :(

Yes there is a way!

First, make a gui button and use the MouseButton1Click event to know when the button is clicked. Then, make a script with a for loop that loops through all of the players in the server and use an if statement to check if the player is equal to the player who clicked the button (in the loop). And if the player is not the player who clicked the button, then get their character and use :BreakJoints()

function killOthers()
    for _, v in pairs(game.Players:GetChildren()) do
         local name = game.Players.LocalPlayer.Name
         if not v.Character.Name == name then
             v.Character.Head:Destroy()
        end
    end
end
yourButtonLink:MouseButton1Down:Connect(killOthers)

This should work(i haven't tested yet)

script.Parent.MouseButton1Down:connect(function()
    for i,v in pairs(game.Players:GetChildren()) do
        if v ~= script.Parent.Parent.Parent then
            v.Character.Humanoid.Health = 0
        end
    end
end)