There are 2 Spoiler things. One does it inline which just grays out the text: Hi! Select your text and then click the ellipsis (3 dots thingy) and select Inline Spoiler.
The other one is maybe for bigger things that you can hide behind a small placeholder:
LOTSA BIG STUFF THAT GOTS HIDDEN AND JUNK
It behind the ellipsis again under Spoiler. LOL ninja'd by @Starry Junimo
There are 2 Spoiler things. One does it inline which just grays out the text: Hi! Select your text and then click the ellipsis (3 dots thingy) and select Inline Spoiler.
The other one is maybe for bigger things that you can hide behind a small placeholder:
LOTSA BIG STUFF THAT GOTS HIDDEN AND JUNK
It behind the ellipsis again under Spoiler. LOL ninja'd by @Starry Junimo