Please install both the content plugin and the editor button plugin. The editor button plugin will put the button below the text editor, and the content plugin will turn the article code into a gallery when the article is viewed in the frontend.
Press the gallery button below the editor to insert some code for a gallery...
The pop up will give a range of options. The ‘search child categories’ option determines whether the plugin should look at child categories of the selected category when selecting images.
Press Save and Close and the code will appear in the article. Save the article, and the gallery will appear in the frontend of the website. If the code appears in the frontend of the website, please make sure you have both the content plugin installed and enabled, as well as the editor button plugin.