Arduino Flow Alarm

I'm trying to build a flow alarm and I'm very new to coding in C++. If it works I would like it to set off an LED when the flow slows or stops. Could anybody suggest a video or website. Thank you in advance.

Flow of what?

Before picking out and hooking up the flow meter, get an Arduino and work your way through the simple examples that come with it.

Learn the programming language, read a switch, a voltage, a sensor, light an LED, etc. Save yourself a lot of frustration!

Flow of vehicle traffic?
Flow of air?
Flow of water in a pipe?
Flow of the river?
Flow of the mud on a mountain slope?
Flow of the text of this post?
Flow of electrons in a wire?

I am not sure what sensor to use to measure the flow of ideas but it may be easier to note the silence and infer a lack of such a flow

Lota of water flow zenzors available.
Read 0 to 1000
Below 10 infers no flow.
Easy to make alarmwiork with that