There are three ways to do it. Click on the symbol to the right of the eraser. A pop up will ask you to select the BBcode that you want to use. Select spoiler and a text box pops up where you can type the text that you want to spoilerize. Click ok and the text is spoiler boxed. The second way is to type the sentence first and then highlight it, click on the symbol and select spoiler. The text is transposed into the text box and then you hit OK. The third way is to type the spoiler tags out manually [ spoiler] [ /spoiler]. Take the space out between the first bracket and the word in order for it to work.