What is the correct way of triggering code if a part is touched?

The issue here is the wrapping of the function. An arguments list ends when a ) is added. If you look at the line where the function gets connected in the event's :Connect function, you'll see the arguments list end before the first line of the code you want to wrap. Everything else is fine, you simply need to remove the ) of the :Connect.

Hey i think this will be the answer to your question. Also your code looks messy but you can tidy them up by doing like i did.

local seat = script.Parent
local Break = false

seat.Touched:Connect(function() -- Sets up an event that sets break to true
    Break = true
end

seat.TouchEnded:Connect(function())

    local count = 0
    Break = false -- Resets the value when you leave the seat

    while count < 30 do

        if Break then -- breaks from the loop if Break = true
            break
        end

        if count == 30 then
            game.Workspace.Tank:Destroy()
        end

    count = count + 1
    wait(0.5)

    end

end) 

local Seat = script.Parent
local Count = 30
local IsTouching = false

seat.Touched:Connect(function()
    Count = 30 -- Reset time
    IsTouching = true
end)

seat.TouchEnded:Connect(function()
    IsTouching = false -- Make it false

    while wait(1) do -- Every 1 second
        if IsTouching == false then -- Detect if IsTouching == false, if not it obviously does not pass the statement
            Count -= 1 -- Minus one
        end
    end

    Count.Changed:Connect(function() -- Count changed
        if Count <= 0 then -- If count equal or lower than 0
            game.Workspace.Tank:Destroy() -- Destroy tank
        end
    end
end)