All of your questions are related, actually.
Consider that there are two types of event conditions: triggered events and continuous events.
Triggered events, identified by the little green arrow symbol next to them, like "on touched", happen once. As soon as the player touches the object, the actions are taken once.
Continuous events monitor the conditions all the time (every tick, technically) to see if they are being met, and if they are, the actions take place all the time as well.
Here's an example of the difference between the two:
Say I have a monster, and I want to do damage to that monster every time I tap on it with the touch screen. Let's call it 50 damage. On touched object, I'd subtract 50 from its hit points. But that would require the player to tap many times, each time they do so, 50HP would be deducted. If I wanted the player to have access to a weaker continuous attack, I'd use the Is touching object action, and would perhaps deduct 5 hit points continuously (every tick) while that's happening.
To answer your question, you would typically use every tick as its own action. Like, every tick -> set text to Monster.HitPoints.
Trigger once is a special kind of event condition. It's a way of turning a continuous action into a triggered one - one that only activates a single time while true. You use this when you need to continuously check for something, but only want its action to take place a single time.