How do I make a spoiler .. Like Im gonna sell a art head texture , so how can I put it in the spoiler ?

Select the text (or img) you want to spoil and then click on , and type a text that you want to appear, like

Yea, but I want my head to appear there

NoGood already told you how to do it.

Upload your head picture to any free image hoster like imgur.com
Once you've done come here and click on this , a box will pop up, insert the url of your picture there.
Then select all the code you have just dragging your mouse over it.
Click on put the name you want to appear like "Hello" for instance, and thats all.

It will look like this