Imagine you have a diary and every time something important happens in your day, you write it in the diary to remember it later. That way you can look back at it and remember what happened.
Now, let's pretend we have a machine that does the same thing, but instead of a diary, it writes down what's happening on a computer. We call this machine a "logging machine".
A log trigger is like a special button that tells the logging machine when to write down what's happening. It's a way to make sure that certain events are recorded in the log.
For example, imagine you're playing a video game and you want to see how long it takes you to beat a certain level. You could set up a log trigger that records the exact time you start the level and the exact time you finish it. That way you can look back at the log and see how long it took you.
So, a log trigger is just a way to make sure important events are recorded in a log, kind of like how you write important things in your diary.