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: