Now that the feature is here, all you need to do is tap the photo icon in the tweet composer and add the media of your choice. The content you add appears side by side or in a grid-like format, depending on how many images, videos, or GIFs you add. You can see what this might look like in this one tweets shared by Twitter.
When I tried the feature myself, I found that you can add up to four pieces of content in total. However, it is unclear whether tweets shared outside the platform will support this feature. I’ve included Twitter’s multimedia tweet in this post, but it only shows one of the two pieces of content included in the tweet and looked the same when I shared it with my colleagues on Slack.