Collapsing and expanding columns html code?

[?? ????l?t / ???? ??]

I don't know the html code for collapsing and expanding columns (eg. when on a site, there is a spoiler, and you have the option to click on the writing to make some writing appear on the same page [expanding], and then you have the option to click on it again to make the writing disappear [collapsing]), is there a site where I can find the right coding for this?

Thank you.