All articles have the gallery-function in it.
You don't need to use that substitution usage for what you're trying to do. Edit CB Gallery Bot in Extensions > Plugins then review the parameters under the Gallery tab where you can enable article galleries.
I don't want folders in the articles.
The below usage is correct, but you need to be careful when using a WYSIWYG editor as it tends to html encode the string breaking the substitution usage. Specifically the quotes get escaped. Switch to editing the source (usually a View Source button) to stop the editor from doing that.
[cbgallery:gallery folders="false" /]