For the spoiler button you use bbcode [spoiler][/spoiler]
For pictures any image hosting website, I use https://imgbb.com/
To embed the picture you use bbcode [img][/img]
You need Adobe Photoshop or some other graphics editor. Then you just put some images over the other, add text and borders here and there. I honestly don't know how to explain better because I learned by trying whatever came to my mind.
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For pictures any image hosting website, I use https://imgbb.com/
To embed the picture you use bbcode [img][/img]
So if you put something like this in your "About Me (Classic)" in profile settings
[spoiler][img]https://cdn.myanimelist.net/images/characters/15/422033.jpg[/img][/spoiler]
It will look like this on your profile: