How would you explain the conduction of an action potential and release of neurotransmitters in the brain to your young brother or sister?
How young is your sibling? How much detail do you want to include? Your explanation will vary depending on your answers to these questions. Here is a start.
At the very simplest level, you could use the example of a wire. Once this wire is stimulated enough, it sends an impulse, which causes the release of some chemicals at one end of the wire. This chemical, in turn, can stimulate the next wire to fire.
However, some chemicals keep the next wire from firing. Since many different wires can stimulate any one wire, the total effect of the helping and hindering chemicals released determine if that one wire will fire.
I hope this helps. Thanks for asking.