First you put the word "trigger" inside square brackets, like this. [ trigger]
I inserted a space, so it would be visible, but you would do it without the space.
Next you type the potentially triggering part.
Then you put "/trigger" inside square brackets, like this, except without the space. [ /trigger]
Adding spaces to make it visible, I type:
[ trigger]This should come up as a trigger code.[ /trigger]
Without the spaces: