In that case, please see the usage of the Block Grid shortcode at https://theme.co/apex/forum/t/shortcodes-block-grid/149. I previously have given the link.
If you're using Cornerstone, the Block Grid is also available as an element. It's the Classic Block Grid.
Just drag and drop the element to the content and edit each Grid Item. You can add an image in the Grid Content using the Rich Text editor.
For more details about Cornerstone usage, please see our Knowledge Base.