If you have a set of similar assets, you may want to create a group instead of having them all show side by side. You do this by selecting multiple assets and clicking "Group assets", under the More button.
In the thumbnail overview, assets that are part of a group is indicated by an icon:
When looking at the asset detail, any grouped assets will be shown with smaller thumbnails below the main image:
To see metadata details for a grouped asset, simply double-click on it. By hovering over a grouped asset you can either remove it from the group or promote it to parent asset.
Remove / add
If you open a grouped folder you can remove media or make any media in the group the parent.
If you want to add more media to the group you just mark the group and the media you want to add, click on more and then group media.