Simple Bot - On Trigger
Simple Bots are typically for a simple 1 trigger actions. They are not always monitoring, and are only activated once a trigger is being fired.
On Trigger Bot
On Trigger bot allows me to run a flow of actions once a new item is created in my data source.
A simple example can be - Send a notification when a new row is added to a Google-sheet document.
See the video on how to do that.