The "Backdrop" feature is only available on the iPhone and Android Instagram app, not the desktop version. Once you have the app downloaded, you'll need to sign in to get started. 

From your Instagram homepage, swipe right or click on your profile picture at the top left-hand corner to create a story the same way you regularly would. Then, select the photo you want to share. 

The Backdrop icon will be found next to the text icon on the top banner. Once you click it, the feature will process your photo and will automatically highlight different areas of your photo. Then, you can select which parts of the photo you'd like to keep when generating a new backdrop. In my example, I selected my puppy, his toy, and his cute fluffy blanket. 

You will have the option to enter a prompt in English of what you'd like the new background to see. It can be as elaborate or simple as you'd like. In my case, I just wanted the background to be light pink, so I typed in "baby pink background." 

Once you enter your prompt, you can select either option or tap on the restart button to generate new results from the same prompt. If you'd rather tweak the prompt, you can click on your old prompt to tweak it or type a new one. When you are satisfied with the results, you can hit next. 

You can now edit your new photo like any other photo, adding text, stickers, and music as you'd like. Once you are done, you can share the photo with your followers and post it.