When you make a post, hit the green Post Reply button and paste in your text. Highlight the text you want to spoil in a block and then click the white square button next to the image, hyperlink, and youtube video buttons. That will spoil the text. If you want to do it another way, hit the white square spoiler button once, paste in your text, and hit it again to signify the end of the spoil zone. Hope this helps.