@VegasRam I'll put something in the FAQ.
But, its the "+" on the top right of the reply box. Press "+", then "Spoiler", then type the title that appears before the spoiler. See photo.
Once it inserts into your reply box continue typing between the bracket symbols (where your cursor appears) the actual spoiler.
Once you press reply, the actual spoiler will appear graphically.
Feel free to test in the testing area.
Thank you for asking the question. If you didn't know, you're not the only one.